Ontological

Ontology is the philosophical study of being. It is traditionally understood as the subdiscipline of metaphysics focused on the most general features of reality. As one of the most fundamental concepts, being encompasses all of reality and every entity within it. To articulate the basic structure of being, ontology examines the commonalities among all things and investigates their classification into basic types, such as the categories of particulars and universals. Particulars are unique, non-repeatable entities, such as the person Socrates, whereas universals are general, repeatable entities, like the color green. Another distinction exists between concrete objects existing in space and time, such as a tree, and abstract objects existing outside space and time, like the number 7. Systems of categories aim to provide a comprehensive inventory of reality by employing categories such as substance, property, relation, state of affairs, and event.

Ontologists disagree regarding which entities exist at the most basic level. Platonic realism asserts that universals have objective existence, while conceptualism maintains that universals exist only in the mind, and nominalism denies their existence altogether. Similar disputes pertain to mathematical objects, unobservable objects assumed by scientific theories, and moral facts. Materialism posits that fundamentally only matter exists, whereas dualism asserts that mind and matter are independent principles. According to some ontologists, objective answers to ontological questions do not exist, with perspectives shaped by differing linguistic practices.

Ontology employs diverse methods of inquiry, including the analysis of concepts and experience, the use of intuitions and thought experiments, and the integration of findings from natural science. Formal ontology investigates the most abstract features of objects, while Applied ontology utilizes ontological theories and principles to study entities within specific domains. For example, social ontology examines basic concepts used in the social sciences. Applied ontology is particularly relevant to information and computer science, which develop conceptual frameworks of limited domains. These frameworks facilitate the structured storage of information, such as in a college database tracking academic activities. Ontology is also pertinent to the fields of logic, theology, and anthropology.

The origins of ontology lie in the ancient period with speculations about the nature of being and the source of the universe, including ancient Indian, Chinese, and Greek philosophy. In the modern period, philosophers conceived ontology as a distinct academic discipline and coined its name.

Definition

Ontology is the study of being. It is the branch of philosophy that investigates the nature of existence, the features all entities have in common, and how they are divided into basic categories of being. It aims to discover the foundational building blocks of the world and characterize reality as a whole in its most general aspects. In this regard, ontology contrasts with individual sciences like biology and astronomy, which restrict themselves to a limited domain of entities, such as living entities and celestial phenomena. In some contexts, the term ontology refers not to the general study of being but to a specific ontological theory within this discipline. It can also mean an inventory or a conceptual scheme of a particular domain, such as the ontology of genes. In this context, an inventory is a comprehensive list of elements. A conceptual scheme is a framework of the key concepts and their relationships.

Ontology is closely related to metaphysics but the exact relation of these two disciplines is disputed. A traditionally influential characterization asserts that ontology is a subdiscipline of metaphysics. According to this view, metaphysics is the study of various aspects of fundamental reality, whereas ontology restricts itself to the most general features of reality. This view sees ontology as general metaphysics, which is to be distinguished from special metaphysics focused on more specific subject matters, like God, mind, and value. A different conception understands ontology as a preliminary discipline that provides a complete inventory of reality while metaphysics examines the features and structure of the entities in this inventory. Another conception says that metaphysics is about real being while ontology examines possible being or the concept of being. It is not universally accepted that there is a clear boundary between metaphysics and ontology. Some philosophers use both terms as synonyms.

The etymology of the word ontology traces back to the ancient Greek terms ὄντως (ontos, meaning 'being') and λογία (logia, meaning 'study of'), literally, 'the study of being'. The ancient Greeks did not use the term ontology, which was coined by philosophers in the 17th century.

Basic concepts

Being

The scope of ontology covers diverse entities, including everyday objects, living beings, celestial bodies, ideas, numbers, and fictional creatures.

Being, or existence, is the main topic of ontology. It is one of the most general and fundamental concepts, encompassing all of reality and every entity within it. In its broadest sense, being only contrasts with non-being or nothingness. It is controversial whether a more substantial analysis of the concept or meaning of being is possible. One proposal understands being as a property possessed by every entity. Critics argue that a thing without being cannot have properties. This means that properties presuppose being and cannot explain it. Another suggestion is that all beings share a set of essential features. According to the Eleatic principle, "power is the mark of being", meaning that only entities with causal influence truly exist. A controversial proposal by philosopher George Berkeley suggests that all existence is mental. He expressed this immaterialism in his slogan "to be is to be perceived".

Depending on the context, the term being is sometimes used with a more limited meaning to refer only to certain aspects of reality. In one sense, being is unchanging and permanent, in contrast to becoming, which implies change. Another contrast is between being, as what truly exists, and phenomena, as what appears to exist. In some contexts, being expresses the fact that something is while essence expresses its qualities or what it is like.

Ontologists often divide being into fundamental classes or highest kinds, called categories of being. Proposed categories include substance, property, relation, state of affairs, and event. They can be used to provide systems of categories, which offer a comprehensive inventory of reality in which every entity belongs to exactly one category. Some philosophers, like Aristotle, say that entities belonging to different categories exist in distinct ways. Others, like John Duns Scotus, insist that there are no differences in the mode of being, meaning that everything exists in the same way. A related dispute is whether some entities have a higher degree of being than others, an idea already found in Plato's work. The more common view in contemporary philosophy is that a thing either exists or not with no intermediary states or degrees.

The relation between being and non-being is a frequent topic in ontology. Influential issues include the status of nonexistent objects and why there is something rather than nothing.

Particulars and universals

The Taj Mahal is a particular entity while the color green is a universal entity.

A central distinction in ontology is between particular and universal entities. Particulars, also called individuals, are unique, non-repeatable entities, like Socrates, the Taj Mahal, and Mars. Universals are general, repeatable entities, like the color green, the form circularity, and the virtue courage. Universals express aspects or features shared by particulars. For example, Mount Everest and Mount Fuji are particulars characterized by the universal mountain.

Universals can take the form of properties or relations. Properties describe the characteristics of things. They are features or qualities possessed by an entity. Properties are often divided into essential and accidental properties. A property is essential if an entity must have it; it is accidental if the entity can exist without it. For instance, having three sides is an essential property of a triangle, whereas being red is an accidental property. Relations are ways how two or more entities stand to one another. Unlike properties, they apply to several entities and characterize them as a group. For example, being a city is a property while being east of is a relation, as in "Kathmandu is a city" and "Kathmandu is east of New Delhi". Relations are often divided into internal and external relations. Internal relations depend only on the properties of the objects they connect, like the relation of resemblance. External relations express characteristics that go beyond what the connected objects are like, such as spatial relations.

Substances play an important role in the history of ontology as the particular entities that underlie and support properties and relations. They are often considered the fundamental building blocks of reality that can exist on their own, while entities like properties and relations cannot exist without substances. Substances persist through changes as they acquire or lose properties. For example, when a tomato ripens, it loses the property green and acquires the property red.

States of affairs are complex particular entities that have several other entities as their components. The state of affairs "Socrates is wise" has two components: the individual Socrates and the property wise. States of affairs that correspond to reality are called facts. Facts are truthmakers of statements, meaning that whether a statement is true or false depends on the underlying facts.

Events are particular entities that occur in time, like the fall of the Berlin Wall and the first moon landing. They usually involve some kind of change, like the lawn becoming dry. In some cases, no change occurs, like the lawn staying wet. Complex events, also called processes, are composed of a sequence of events.

Concrete and abstract objects

Concrete objects are entities that exist in space and time, such as a tree, a car, and a planet. They have causal powers and can affect each other, like when a car hits a tree and both are deformed in the process. Abstract objects, by contrast, are outside space and time, such as the number 7 and the set of integers. They lack causal powers and do not undergo changes. The existence and nature of abstract objects remain subjects of philosophical debate.

Concrete objects encountered in everyday life are complex entities composed of various parts. For example, a book is made up of two covers and the pages between them. Each of these components is itself constituted of smaller parts, like molecules, atoms, and elementary particles.Mereology studies the relation between parts and wholes. One position in mereology says that every collection of entities forms a whole. According to another view, this is only the case for collections that fulfill certain requirements, for instance, that the entities in the collection touch one another. The problem of material constitution asks whether or in what sense a whole should be considered a new object in addition to the collection of parts composing it.

Abstract objects are closely related to fictional and intentional objects. Fictional objects are entities invented in works of fiction. They can be things, like the One Ring in J. R. R. Tolkien's book series The Lord of the Rings, and people, like the Monkey King in the novel Journey to the West. Some philosophers say that fictional objects are abstract objects and exist outside space and time. Others understand them as artifacts that are created as the works of fiction are written. Intentional objects are entities that exist within mental states, like perceptions, beliefs, and desires. For example, if a person thinks about the Loch Ness Monster then the Loch Ness Monster is the intentional object of this thought. People can think about existing and non-existing objects. This makes it difficult to assess the ontological status of intentional objects.

Other concepts

Ontological dependence is a relation between entities. An entity depends ontologically on another entity if the first entity cannot exist without the second entity. For instance, the surface of an apple cannot exist without the apple. An entity is ontologically independent if it does not depend on anything else, meaning that it is fundamental and can exist on its own. Ontological dependence plays a central role in ontology and its attempt to describe reality on its most fundamental level. It is closely related to metaphysical grounding, which is the relation between a ground and the facts it explains.

Willard Van Orman Quine used the concept of ontological commitments to analyze theories.

An ontological commitment of a person or a theory is an entity that exists according to them. For instance, a person who believes in God has an ontological commitment to God. Ontological commitments can be used to analyze which ontologies people explicitly defend or implicitly assume. They play a central role in contemporary metaphysics when trying to decide between competing theories. For example, the Quine–Putnam indispensability argument defends mathematical Platonism, asserting that numbers exist because the best scientific theories are ontologically committed to numbers.

Possibility and necessity are further topics in ontology. Possibility describes what can be the case, as in "it is possible that extraterrestrial life exists". Necessity describes what must be the case, as in "it is necessary that three plus two equals five". Possibility and necessity contrast with actuality, which describes what is the case, as in "Doha is the capital of Qatar". Ontologists often use the concept of possible worlds to analyze possibility and necessity. A possible world is a complete and consistent way how things could have been. For example, Haruki Murakami was born in 1949 in the actual world but there are possible worlds in which he was born at a different date. Using this idea, possible world semantics says that a sentence is possibly true if it is true in at least one possible world. A sentence is necessarily true if it is true in all possible worlds.

In ontology, identity means that two things are the same. Philosophers distinguish between qualitative and numerical identity. Two entities are qualitatively identical if they have exactly the same features, such as perfect identical twins. This is also called exact similarity and indiscernibility. Numerical identity, by contrast, means that there is only a single entity. For example, if Fatima is the mother of Leila and Hugo then Leila's mother is numerically identical to Hugo's mother. Another distinction is between synchronic and diachronic identity. Synchronic identity relates an entity to itself at the same time. Diachronic identity relates an entity to itself at different times, as in "the woman who bore Leila three years ago is the same woman who bore Hugo this year".

Branches

There are different and sometimes overlapping ways to divide ontology into branches. Pure ontology focuses on the most abstract topics associated with the concept and nature of being. It is not restricted to a specific domain of entities and studies existence and the structure of reality as a whole. Pure ontology contrasts with applied ontology, also called domain ontology. Applied ontology examines the application of ontological theories and principles to specific disciplines and domains, often in the field of science. It considers ontological problems in regard to specific entities such as matter, mind, numbers, God, and cultural artifacts.

Social ontology, a major subfield of applied ontology, studies social kinds, like money, gender, society, and language. It aims to determine the nature and essential features of these concepts while also examining their mode of existence. According to a common view, social kinds are useful constructions to describe the complexities of social life. This means that they are not pure fictions but, at the same time, lack the objective or mind-independent reality of natural phenomena like elementary particles, lions, and stars. In the fields of computer science, information science, and knowledge representation, applied ontology is interested in the development of formal frameworks to encode and store information about a limited domain of entities in a structured way. A related application in genetics is Gene Ontology, which is a comprehensive framework for the standardized representation of gene-related information across species and databases.

Formal ontology is the study of objects in general while focusing on their abstract structures and features. It divides objects into different categories based on the forms they exemplify. Formal ontologists often rely on the tools of formal logic to express their findings in an abstract and general manner. Formal ontology contrasts with material ontology, which distinguishes between different areas of objects and examines the features characteristic of a specific area. Examples are ideal spatial beings in the area of geometry and living beings in the area of biology.

Descriptive ontology aims to articulate the conceptual scheme underlying how people ordinarily think about the world. Prescriptive ontology departs from common conceptions of the structure of reality and seeks to formulate a new and better conceptualization.

Another contrast is between analytic and speculative ontology. Analytic ontology examines the types and categories of being to determine what kinds of things could exist and what features they would have. Speculative ontology aims to determine which entities actually exist, for example, whether there are numbers or whether time is an illusion.

Martin Heidegger proposed fundamental ontology to study the meaning of being.

Metaontology studies the underlying concepts, assumptions, and methods of ontology. Unlike other forms of ontology, it does not ask "what exists" but "what does it mean for something to exist" and "how can people determine what exists". It is closely related to fundamental ontology, an approach developed by philosopher Martin Heidegger that seeks to uncover the meaning of being.

Schools of thought

Realism and anti-realism

The term realism is used for various theories that affirm that some kind of phenomenon is real or has mind-independent existence. Ontological realism is the view that there are objective facts about what exists and what the nature and categories of being are. Ontological realists do not make claims about what those facts are, for example, whether elementary particles exist. They merely state that there are mind-independent facts that determine which ontological theories are true. This idea is denied by ontological anti-realists, also called ontological deflationists, who say that there are no substantive facts one way or the other. According to philosopher Rudolf Carnap, for example, ontological statements are relative to language and depend on the ontological framework of the speaker. This means that there are no framework-independent ontological facts since different frameworks provide different views while there is no objectively right or wrong framework.

Plato (left) and Aristotle (right) disagreed on whether universals can exist without matter.

In a more narrow sense, realism refers to the existence of certain types of entities. Realists about universals say that universals have mind-independent existence. According to Platonic realists, universals exist not only independent of the mind but also independent of particular objects that exemplify them. This means that the universal red could exist by itself even if there were no red objects in the world. Aristotelian realism, also called moderate realism, rejects this idea and says that universals only exist as long as there are objects that exemplify them. Conceptualism, by contrast, is a form of anti-realism, stating that universals only exist in the mind as concepts that people use to understand and categorize the world. Nominalists defend a strong form of anti-realism by saying that universals have no existence. This means that the world is entirely composed of particular objects.

Mathematical realism, a closely related view in the philosophy of mathematics, says that mathematical facts exist independently of human language, thought, and practices and are discovered rather than invented. According to mathematical Platonism, this is the case because of the existence of mathematical objects, like numbers and sets. Mathematical Platonists say that mathematical objects are as real as physical objects, like atoms and stars, even though they are not accessible to empirical observation. Influential forms of mathematical anti-realism include conventionalism, which says that mathematical theories are trivially true simply by how mathematical terms are defined, and game formalism, which understands mathematics not as a theory of reality but as a game governed by rules of string manipulation.

Modal realism is the theory that in addition to the actual world, there are countless possible worlds as real and concrete as the actual world. The primary difference is that the actual world is inhabited by us while other possible worlds are inhabited by our counterparts. Modal anti-realists reject this view and argue that possible worlds do not have concrete reality but exist in a different sense, for example, as abstract or fictional objects.

Scientific realists say that the scientific description of the world is an accurate representation of reality. It is of particular relevance in regard to things that cannot be directly observed by humans but are assumed to exist by scientific theories, like electrons, forces, and laws of nature. Scientific anti-realism says that scientific theories are not descriptions of reality but instruments to predict observations and the outcomes of experiments.

Moral realists claim that there exist mind-independent moral facts. According to them, there are objective principles that determine which behavior is morally right. Moral anti-realists either claim that moral principles are subjective and differ between persons and cultures, a position known as moral relativism, or outright deny the existence of moral facts, a view referred to as moral nihilism.

By number of categories

Monocategorical theories say that there is only one fundamental category, meaning that every single entity belongs to the same universal class. For example, some forms of nominalism state that only concrete particulars exist while some forms of bundle theory state that only properties exist. Polycategorical theories, by contrast, hold that there is more than one basic category, meaning that entities are divided into two or more fundamental classes. They take the form of systems of categories, which list the highest genera of being to provide a comprehensive inventory of everything.

The closely related discussion between monism and dualism is about the most fundamental types that make up reality. According to monism, there is only one kind of thing or substance on the most basic level.Materialism is an influential monist view; it says that everything is material. This means that mental phenomena, such as beliefs, emotions, and consciousness, either do not exist or exist as aspects of matter, like brain states. Idealists take the converse perspective, arguing that everything is mental. They may understand physical phenomena, like rocks, trees, and planets, as ideas or perceptions of conscious minds.Neutral monism occupies a middle ground by saying that both mind and matter are derivative phenomena. Dualists state that mind and matter exist as independent principles, either as distinct substances or different types of properties. In a slightly different sense, monism contrasts with pluralism as a view not about the number of basic types but the number of entities. In this sense, monism is the controversial position that only a single all-encompassing entity exists in all of reality. Pluralism is more commonly accepted and says that several distinct entities exist.

By fundamental categories

The historically influential substance-attribute ontology is a polycategorical theory. It says that reality is at its most fundamental level made up of unanalyzable substances that are characterized by universals, such as the properties an individual substance has or relations that exist between substances. The closely related to substratum theory says that each concrete object is made up of properties and a substratum. The difference is that the substratum is not characterized by properties: it is a featureless or bare particular that merely supports the properties.

Various alternative ontological theories have been proposed that deny the role of substances as the foundational building blocks of reality. Stuff ontologies say that the world is not populated by distinct entities but by continuous stuff that fills space. This stuff may take various forms and is often conceived as infinitely divisible. According to process ontology, processes or events are the fundamental entities. This view usually emphasizes that nothing in reality is static, meaning that being is dynamic and characterized by constant change. Bundle theories state that there are no regular objects but only bundles of co-present properties. For example, a lemon may be understood as a bundle that includes the properties yellow, sour, and round. According to traditional bundle theory, the bundled properties are universals, meaning that the same property may belong to several different bundles. According to trope bundle theory, properties are particular entities that belong to a single bundle.

Some ontologies focus not on distinct objects but on interrelatedness. According to relationalism, all of reality is relational at its most fundamental level.Ontic structural realism agrees with this basic idea and focuses on how these relations form complex structures. Some structural realists state that there is nothing but relations, meaning that individual objects do not exist. Others say that individual objects exist but depend on the structures in which they participate. Fact ontologies present a different approach by focusing on how entities belonging to different categories come together to constitute the world. Facts, also known as states of affairs, are complex entities; for example, the fact that the Earth is a planet consists of the particular object the Earth and the property being a planet. Fact ontologies state that facts are the fundamental constituents of reality, meaning that objects, properties, and relations cannot exist on their own and only form part of reality to the extent that they participate in facts.

In the history of philosophy, various ontological theories based on several fundamental categories have been proposed. One of the first theories of categories was suggested by Aristotle, whose system includes ten categories: substance, quantity, quality, relation, place, date, posture, state, action, and passion. An early influential system of categories in Indian philosophy, first proposed in the Vaisheshika school, distinguishes between six categories: substance, quality, motion, universal, individuator, and inherence.Immanuel Kant's transcendental idealism includes a system of twelve categories, which Kant saw as pure concepts of understanding. They are subdivided into four classes: quantity, quality, relation, and modality. In more recent philosophy, theories of categories were developed by C. S. Peirce, Edmund Husserl, Samuel Alexander, Roderick Chisholm, and E. J. Lowe.

Others

The dispute between constituent and relational ontologies concerns the internal structure of concrete particular objects. Constituent ontologies say that objects have an internal structure with properties as their component parts. Bundle theories are an example of this position: they state that objects are bundles of properties. This view is rejected by relational ontologies, which say that objects have no internal structure, meaning that properties do not inhere in them but are externally related to them. According to one analogy, objects are like pin-cushions and properties are pins that can be stuck to objects and removed again without becoming a real part of objects. Relational ontologies are common in certain forms of nominalism that reject the existence of universal properties.

Hierarchical ontologies state that the world is organized into levels. Entities on all levels are real but low-level entities are more fundamental than high-level entities. This means that they can exist without high-level entities while high-level entities cannot exist without low-level entities. One hierarchical ontology says that elementary particles are more fundamental than the macroscopic objects they compose, like chairs and tables. Other hierarchical theories assert that substances are more fundamental than their properties and that nature is more fundamental than culture. Flat ontologies, by contrast, deny that any entity has a privileged status, meaning that all entities exist on the same level. For them, the main question is only whether something exists rather than identifying the level at which it exists.

The ontological theories of endurantism and perdurantism aim to explain how material objects persist through time. Endurantism is the view that material objects are three-dimensional entities that travel through time while being fully present in each moment. They remain the same even when they gain or lose properties as they change. Perdurantism is the view that material objects are four-dimensional entities that extend not just through space but also through time. This means that they are composed of temporal parts and, at any moment, only one part of them is present but not the others. According to perdurantists, change means that an earlier part exhibits different qualities than a later part. When a tree loses its leaves, for instance, there is an earlier temporal part with leaves and a later temporal part without leaves.

Differential ontology is a poststructuralist approach interested in the relation between the concepts of identity and difference. It says that traditional ontology sees identity as the more basic term by first characterizing things in terms of their essential features and then elaborating differences based on this conception. Differential ontologists, by contrast, privilege difference and say that the identity of a thing is a secondary determination that depends on how this thing differs from other things.

Object-oriented ontology belongs to the school of speculative realism and examines the nature and role of objects. It sees objects as the fundamental building blocks of reality. As a flat ontology, it denies that some entities have a more fundamental form of existence than others. It uses this idea to argue that objects exist independently of human thought and perception.

Methods

Methods of ontology are ways of conducting ontological inquiry and deciding between competing theories. There is no single standard method; the diverse approaches are studied by metaontology.

Conceptual analysis is a method to understand ontological concepts and clarify their meaning. It proceeds by analyzing their component parts and the necessary and sufficient conditions under which a concept applies to an entity. This information can help ontologists decide whether a certain type of entity, such as numbers, exists.Eidetic variation is a related method in phenomenological ontology that aims to identify the essential features of different types of objects. Phenomenologists start by imagining an example of the investigated type. They proceed by varying the imagined features to determine which ones cannot be changed, meaning they are essential. The transcendental method begins with a simple observation that a certain entity exists. In the following step, it studies the ontological repercussions of this observation by examining how it is possible or which conditions are required for this entity to exist.

Another approach is based on intuitions in the form of non-inferential impressions about the correctness of general principles. These principles can be used as the foundation on which an ontological system is built and expanded using deductive reasoning. A further intuition-based method relies on thought experiments to evoke new intuitions. This happens by imagining a situation relevant to an ontological issue and then employing counterfactual thinking to assess the consequences of this situation. For example, some ontologists examine the relation between mind and matter by imagining creatures identical to humans but without consciousness.

Naturalistic methods rely on the insights of the natural sciences to determine what exists. According to an influential approach by Willard Van Orman Quine, ontology can be conducted by analyzing the ontological commitments of scientific theories. This method is based on the idea that scientific theories provide the most reliable description of reality and that their power can be harnessed by investigating the ontological assumptions underlying them.

William of Ockham proposed Ockham's Razor, a principle to decide between competing theories.

Principles of theory choice offer guidelines for assessing the advantages and disadvantages of ontological theories rather than guiding their construction. The principle of Ockham's Razor says that simple theories are preferable. A theory can be simple in different respects, for example, by using very few basic types or by describing the world with a small number of fundamental entities. Ontologists are also interested in the explanatory power of theories and give preference to theories that can explain many observations. A further factor is how close a theory is to common sense. Some ontologists use this principle as an argument against theories that are very different from how ordinary people think about the issue.

In applied ontology, ontological engineering is the process of creating and refining conceptual models of specific domains. Developing a new ontology from scratch involves various preparatory steps, such as delineating the scope of the domain one intends to model and specifying the purpose and use cases of the ontology. Once the foundational concepts within the area have been identified, ontology engineers proceed by defining them and characterizing the relations between them. This is usually done in a formal language to ensure precision and, in some cases, automatic computability. In the following review phase, the validity of the ontology is assessed using test data. Various more specific instructions for how to carry out the different steps have been suggested. They include the Cyc method, Grüninger and Fox's methodology, and so-called METHONTOLOGY. In some cases, it is feasible to adapt a pre-existing ontology to fit a specific domain and purpose rather than creating a new one from scratch.

Related fields

Ontology overlaps with many disciplines, including logic, the study of correct reasoning. Ontologists often employ logical systems to express their insights, specifically in the field of formal ontology. Of particular interest to them is the existential quantifier (${\displaystyle \exists }$), which is used to express what exists. In first-order logic, for example, the formula ${\displaystyle \exists x{\text{Dog}}(x)}$ states that dogs exist. Some philosophers study ontology by examining the structure of thought and language, saying that they reflect the structure of being. Doubts about the accuracy of natural language have led some ontologists to seek a new formal language, termed ontologese, for a better representation of the fundamental structure of reality.

Suggested Upper Merged Ontology

Entity       Physical       Object     Process     Abstract       Quantity     Proposition     Attribute     Relation     Set or Class

Fundamental categories in the Suggested Upper Merged Ontology

Ontologies are often used in information science to provide a conceptual scheme or inventory of a specific domain, making it possible to classify objects and formally represent information about them. This is of specific interest to computer science, which builds databases to store this information and defines computational processes to automatically transform and use it. For instance, to encode and store information about clients and employees in a database, an organization may use an ontology with categories such as person, company, address, and name. In some cases, it is necessary to exchange information belonging to different domains or to integrate databases using distinct ontologies. This can be achieved with the help of upper ontologies, which are not limited to one specific domain. They use general categories that apply to most or all domains, like Suggested Upper Merged Ontology and Basic Formal Ontology.

Similar applications of ontology are found in various fields seeking to manage extensive information within a structured framework. Protein Ontology is a formal framework for the standardized representation of protein-related entities and their relationships.Gene Ontology and Sequence Ontology serve a similar purpose in the field of genetics. Environment Ontology is a knowledge representation focused on ecosystems and environmental processes.Friend of a Friend provides a conceptual framework to represent relations between people and their interests and activities.

The topic of ontology has received increased attention in anthropology since the 1990s, sometimes termed the "ontological turn". This type of inquiry is focused on how people from different cultures experience and understand the nature of being. Specific interest has been given to the ontological outlook of Indigenous people and how it differs from a Western perspective. As an example of this contrast, it has been argued that various indigenous communities ascribe intentionality to non-human entities, like plants, forests, or rivers. This outlook is known as animism and is also found in Native American ontologies, which emphasize the interconnectedness of all living entities and the importance of balance and harmony with nature.

Ontology is closely related to theology and its interest in the existence of God as an ultimate entity. The ontological argument, first proposed by Anselm of Canterbury, attempts to prove the existence of the divine. It defines God as the greatest conceivable being. From this definition it concludes that God must exist since God would not be the greatest conceivable being if God lacked existence. Another overlap in the two disciplines is found in ontological theories that use God or an ultimate being as the foundational principle of reality. Heidegger criticized this approach, terming it ontotheology.

History

Kapila was one of the founding fathers of the dualist school of Samkhya.

The roots of ontology in ancient philosophy are speculations about the nature of being and the source of the universe. Discussions of the essence of reality are found in the Upanishads, ancient Indian scriptures dating from as early as 700 BCE. They say that the universe has a divine foundation and discuss in what sense ultimate reality is one or many.Samkhya, the first orthodox school of Indian philosophy, formulated an atheist dualist ontology based on the Upanishads, identifying pure consciousness and matter as its two foundational principles. The later Vaisheshika school proposed a comprehensive system of categories. In ancient China, Laozi's (6th century BCE)Taoism examines the underlying order of the universe, known as Tao, and how this order is shaped by the interaction of two basic forces, yin and yang. The philosophical movement of Xuanxue emerged in the 3rd century CE and explored the relation between being and non-being.

Starting in the 6th century BCE, Presocratic philosophers in ancient Greece aimed to provide rational explanations of the universe. They suggested that a first principle, such as water or fire, is the primal source of all things.Parmenides (c. 515–450 BCE) is sometimes considered the founder of ontology because of his explicit discussion of the concepts of being and non-being. Inspired by Presocratic philosophy, Plato (427–347 BCE) developed his theory of forms. It distinguishes between unchangeable perfect forms and matter, which has a lower degree of existence and imitates the forms.Aristotle (384–322 BCE) suggested an elaborate system of categories that introduced the concept of substance as the primary kind of being. The school of Neoplatonism arose in the 3rd century CE and proposed an ineffable source of everything, called the One, which is more basic than being itself.

The problem of universals was an influential topic in medieval ontology. Boethius (477–524 CE) suggested that universals can exist not only in matter but also in the mind. This view inspired Peter Abelard (1079–1142 CE), who proposed that universals exist only in the mind.Thomas Aquinas (1224–1274 CE) developed and refined fundamental ontological distinctions, such as the contrast between existence and essence, between substance and accidents, and between matter and form. He also discussed the transcendentals, which are the most general properties or modes of being.John Duns Scotus (1266–1308) argued that all entities, including God, exist in the same way and that each entity has a unique essence, called haecceity.William of Ockham (c. 1287–1347 CE) proposed that one can decide between competing ontological theories by assessing which one uses the smallest number of elements, a principle known as Ockham's razor.

The Neo-Confucian philosopher Zhu Xi conceived the concept of li as the organizing principle of the universe.

In Arabic-Persian philosophy, Avicenna (980–1037 CE) combined ontology with theology. He identified God as a necessary being that is the source of everything else, which only has contingent existence. In 8th-century Indian philosophy, the school of Advaita Vedanta emerged. It says that only a single all-encompassing entity exists, stating that the impression of a plurality of distinct entities is an illusion. Starting in the 13th century CE, the Navya-Nyāya school built on Vaisheshika ontology with a particular focus on the problem of non-existence and negation. 9th-century China saw the emergence of Neo-Confucianism, which developed the idea that a rational principle, known as li, is the ground of being and order of the cosmos.

René Descartes (1596–1650) formulated a dualist ontology at the beginning of the modern period. It distinguishes between mind and matter as distinct substances that causally interact. Rejecting Descartes's dualism, Baruch Spinoza (1632–1677) proposed a monist ontology according to which there is only a single entity that is identical to God and nature.Gottfried Wilhelm Leibniz (1646–1716), by contrast, said that the universe is made up of many simple substances, which are synchronized but do not interact with one another.John Locke (1632–1704) proposed his substratum theory, which says that each object has a featureless substratum that supports the object's properties.Christian Wolff (1679–1754) was influential in establishing ontology as a distinct discipline, delimiting its scope from other forms of metaphysical inquiry.George Berkeley (1685–1753) developed an idealist ontology according to which material objects are ideas perceived by minds.

Immanuel Kant (1724–1804) rejected the idea that humans can have direct knowledge of independently existing things and their nature, limiting knowledge to the field of appearances. For Kant, ontology does not study external things but provides a system of pure concepts of understanding. Influenced by Kant's philosophy, Georg Wilhelm Friedrich Hegel (1770–1831) linked ontology and logic. He said that being and thought are identical and examined their foundational structures.Arthur Schopenhauer (1788–1860) rejected Hegel's philosophy and proposed that the world is an expression of a blind and irrational will.Francis Herbert Bradley (1846–1924) saw absolute spirit as the ultimate and all-encompassing reality while denying that there are any external relations. In Indian philosophy, Swami Vivekananda (1863–1902) expanded on Advaita Vedanta, emphasizing the unity of all existence.Sri Aurobindo (1872–1950) sought to understand the world as an evolutionary manifestation of a divine consciousness.

At the beginning of the 20th century, Edmund Husserl (1859–1938) developed phenomenology and employed its method, the description of experience, to address ontological problems. This idea inspired his student Martin Heidegger (1889–1976) to clarify the meaning of being by exploring the mode of human existence.Jean-Paul Sartre responded to Heidegger's philosophy by examining the relation between being and nothingness from the perspective of human existence, freedom, and consciousness. Based on the phenomenological method, Nicolai Hartmann (1882–1950) developed a complex hierarchical ontology that divides reality into four levels: inanimate, biological, psychological, and spiritual.

Alexius Meinong proposed that there are nonexistent objects.

Alexius Meinong (1853–1920) articulated a controversial ontological theory that includes nonexistent objects as part of being. Arguing against this theory, Bertrand Russell (1872–1970) formulated a fact ontology known as logical atomism. This idea was further refined by the early Ludwig Wittgenstein (1889–1951) and inspired D. M. Armstrong's (1926–2014) ontology.Alfred North Whitehead (1861–1947), by contrast, developed a process ontology.Rudolf Carnap (1891–1970) questioned the objectivity of ontological theories by claiming that what exists depends on one's linguistic framework. He had a strong influence on Willard Van Orman Quine (1908–2000), who analyzed the ontological commitments of scientific theories to solve ontological problems. Quine's student David Lewis (1941–2001) formulated the position of modal realism, which says that possible worlds are as real and concrete as the actual world. Since the end of the 20th century, interest in applied ontology has risen in computer and information science with the development of conceptual frameworks for specific domains.

See also

• Hauntology – Return or persistence of past ideas

References

Notes

1. This focus on general principles rather than specific entities is traditionally expressed in the characterization of ontology as the science of being qua being or being insofar as it is being.
2. When used as a countable noun, a being is the same as an entity.
3. This idea is opposed by trope theorists, who understand properties and relations as particular entities.
4. Other influential distinctions are between intrinsic and extrinsic properties, between determinate or determinable properties, and between categorical and dispositional properties.
5. The term substance has a specific meaning in philosophy distinct from ordinary language expressions such as chemical substance or substance abuse.
6. David Armstrong and his followers use a different terminology that does not distinguish between states of affairs and facts.
7. Some ontologists also use the term in a less common sense to refer to universals in the form of event types.
8. The precise definition is disputed.
9. The idea of formal ontology was first formulated by phenomenologist Edmund Husserl, who studied objects in general by relying on fundamental categories such as unity, plurality, state of affairs, part, and whole. He examined the relations between these categories and how they depend on one another.
10. They are usually distinguished by combining them with a qualifier to express which type is meant, as in ontological realism, mathematical realism, and moral realism. The qualifiers are sometimes left out if the meaning is clear in the context.
11. The exact definition of the term is disputed.
12. According to some pantheists, this entity is God.
13. This view contrasts with atomism, which states that the world is composed of discrete, indivisible units.
14. For example, relationalism about spacetime says that space and time are nothing but relations. Spacetime substantivalists reject this view and state that spacetime is a distinct object rather than a relational structure between objects.
15. This is expressed in a slogan by Ludwig Wittgenstein: "The world is the totality of facts, not of things".
16. In this context, the term "relational ontology" has a slightly different meaning than the term "relationalism", which says that, at the most basic level, reality is made up of relations.
17. Some flat ontologies allow that there are entities on higher levels but stipulate that they are reducible to the lowest level, meaning that they are no addition to being.
18. For example, it is essential for a triangle to have three sides since it ceases to be a triangle if a fourth side is added.
19. An essential step in Quine's analysis is to translate the theory into first-order logic to make its ontological assumptions explicit.
20. Its initial ideas were developed in the 7th and 6th centuries BCE but it was not until 350 CE that it received its classical and systematic formulation.
21. The founding text of the school was written 500–300 BCE and the first major commentary on it is dated 400 CE.
22. The exact date is disputed and some theorists suggest a later date between the 4th and 3rd centuries BCE.

Citations

1. • Lowe 2005, p. 671
   • Campbell 2006, pp. 21–22
   • Craig 1998, Lead Section
2. • Berto & Plebani 2015, p. 1
   • Shields 2014, pp. 279–282
3. • Berto & Plebani 2015, pp. 1–3
   • Campbell 2006, pp. 21–22
   • Effingham 2013, § The Basics: Ontology
4. • Simons 2009, pp. 469–470
   • Merriam-Webster 2024
   • Campbell 2006, pp. 21–22
   • Haritha et al. 2018, p. 489
5. • Lowe 2006, p. 195
   • Tambassi 2017, p. 6
6. • Sankey 2018, § 1.7 Conceptual relativism
   • Grove & Short 1991, p. 211
7. • Berto & Plebani 2015, pp. 3–4
   • Lowe 2005, p. 671
8. • Van Inwagen, Sullivan & Bernstein 2023, § 1. The Word 'Metaphysics' and the Concept of Metaphysics
   • Craig 1998a, § 2. Specific Metaphysics
9. • Berto & Plebani 2015, pp. 4–5
   • Tambassi 2022, p. 79
10. Jaroszyński 2018, p. 6
11. • Berto & Plebani 2015, pp. 3, 5
    • Mulligan 2012, p. x
12. • Berto & Plebani 2015, p. 1
    • Taliaferro & Marty 2018, p. 203
    • Hoad 1993, p. 323
13. Lowe 2005a, p. 84
14. • MacIntyre 2006, p. 527
    • Jaroszyński 2023, pp. 254–255
    • Lowe 2005a, p. 84
    • Jacquette 2014, pp. 1–2, 12–13
15. • MacIntyre 2006, pp. 528–529
    • Jacquette 2014, pp. 1–2, 12–13
16. • MacIntyre 2006, pp. 528–529
    • Casati & Fujikawa, § 2b. Universalism
17. • Nelson 2022, § 1. Frege and Russell: Existence Is Not a Property of Individuals
    • Casati & Fujikawa, § 1. Existence as a Second-Order Property and Its Relation to Quantification
18. Campbell 2006, p. 22
19. • Van Inwagen 2024, p. 280
    • Deutscher 2021, p. 20
20. • MacIntyre 2006, p. 527
    • Zhang 2011, p. 220
    • Hartmann 2012, pp. 46–47
21. MacIntyre 2006, p. 527
22. • Lowe 2005a, p. 84
    • Ceylan 1993, p. 329
23. • Thomasson 2022, Lead Section
    • Loux & Crisp 2017, pp. 11–12
    • Wardy 1998, Lead Section
24. • Campbell 2006, pp. 23–25
    • Hoffman & Rosenkrantz 2008, p. 26
25. • Widder 2009, pp. 32–35
    • LaZella 2019, p. 17
26. • Daly 2009, pp. 227–228
    • Van Inwagen 2023
    • Casati & Fujikawa, §3. How Many Ways of Being Existent?
    • Gibson 1998, pp. 5–8
27. • Reicher 2022, lead section, §1. The Concept of a Nonexistent Object
    • Gibson 1998, p. 8
    • Yao 2014, p. 140
28. • Lowe 2005b, p. 277
    • Casati & Fujikawa, Lead Section, §4. Why Is There Something Rather Than Nothing?
    • Sorensen 2023, Lead Section, §1. Why Is There Something Rather Than Nothing?
    • Pruss & Rasmussen 2018, pp. 4–5
29. • Lowe 2005, p. 683
    • MacLeod & Rubenstein, Lead Section, § 1a. The Nature of Universals
    • Bigelow 1998, Lead Section
    • Campbell 2006, § Particularity and Individuality
    • Maurin 2019, Lead Section
30. • MacLeod & Rubenstein, Lead Section
    • Bigelow 1998a, Lead Section
    • Cowling 2019, Lead Section
    • Loux & Crisp 2017, pp. 17–19
31. • Campbell 2006, pp. 24–25
    • Bigelow 1998, Lead Section
32. Campbell 2006, p. 25
33. • Campbell 2006, p. 24
    • Orilia & Paolini Paoletti 2022, Lead Section
34. Orilia & Paolini Paoletti 2022, § 1.7 Kinds of Properties
35. Vaidya & Wallner 2024, p. 473
36. • Orilia & Paolini Paoletti 2022, § 1.7 Kinds of Properties, § 5.2. Essentially Categorical vs. Essentially Dispositional Properties
    • Marshall & Weatherson 2023, Lead Section
37. • Sider 2010, p. 13
    • Bogen 2005, p. 798
    • MacBride 2020, lead section
    • Campbell 2006, p. 25
38. MacBride 2020, § 2. Eliminativism, External Relations and Bradley’s Regress
39. • MacBride 2020, §1. Preliminary Distinctions
    • Heil 2009, p. 316
    • Armstrong 2010, pp. 24–25
40. O'Conaill 2022, p. 1
41. • Campbell 2006, pp. 23–24
    • O'Conaill 2022, pp. 1–2, 12–13, 29
    • Robinson & Weir 2024, Lead Section
42. • Campbell 2006, p. 25
    • Textor 2021, Lead Section
43. Textor 2021, Lead Section
44. Textor 2021, Lead Section
45. Mackie 2005, p. 272
46. • Mackie 2005, p. 272
    • Campbell 2006, p. 25
47. Campbell 2006, p. 25
48. • Mackie 1998, Lead Section
    • Falguera, Martínez-Vidal & Rosen 2022, lead section, § 1. Introduction
    • Faye 2013, pp. 89–91
    • Prior 2006, pp. 498–499
    • Oliver 2005, p. 3
49. Oliver 2005, p. 3
50. • Oliver 2005, p. 3
    • Plebani 2013, p. 5
51. • Cornell, Lead Section
    • Loux & Crisp 2017, pp. 250–251
    • Varzi 2019, Lead Section, § 1. 'Part' and Parthood
    • Cornell, Lead Section, § 2. The Special Composition Question
    • Tallant 2017, pp. 19–21
52. • Loux & Crisp 2017, pp. 82–83
    • Cornell, Lead Section, § 2. The Special Composition Question
    • Brenner 2015, p. 1295
    • Tallant 2017, pp. 19–21, 23–24, 32–33
    • Cornell, Lead Section
53. • Rea 1997, pp. xv–xvi
    • Korman 2021, Lead Section
54. • Kroon & Voltolini 2023, Lead Section
    • Lamarque 1998, Lead Section
    • Prior 2006, p. 493
55. • Kroon & Voltolini 2023, § 1. The Metaphysics of Fictional Entities
    • Lamarque 1998, § 3. Hospitable theories
56. • Jacob 2023, 2. Intentional inexistence
    • Kriegel 2007, pp. 307–308
    • O’Madagain, § 2. Intentional Objects
57. • Ney 2014, pp. 53–55
    • Fine 1995, pp. 269–270
58. Nuñez Erices 2019, pp. 15–16
59. • Ney 2014, pp. 53–55
    • Fine 1995, pp. 269–270
60. • Tahko & Lowe 2020, § 5. Ontological Dependence and Metaphysical Grounding
    • Ney 2014, pp. 53–55
61. • Ney 2014, p. 31
    • Jubien 1998, Lead Section
62. Jubien 1998, Lead Section
63. • Colyvan 2001, p. 23
    • Bangu 2012, pp. 26–27
    • Ney 2014, pp. 40–43
    • Van Inwagen, Sullivan & Bernstein 2023, § 4. The Methodology of Metaphysics
64. • Parent, Lead Section
    • Loux & Crisp 2017, pp. 149–150
    • Koons & Pickavance 2015, pp. 154–155
    • Mumford 2012, § 8. What Is Possible?
65. • Berto & Jago 2023, Lead Section
    • Pavel 1986, p. 50
66. • Menzel 2023, Lead Section, § 1. Possible Worlds and Modal Logic
    • Kuhn 2010, p. 13
67. • Kirwan 2005, pp. 417–418
    • Noonan & Curtis 2022, Lead Section
    • Kuhlmann 2010, pp. 1867–1867b
68. • Gallois 2016, § 2.1 Diachronic and Synchronic Identity
    • Noonan & Curtis 2022, Lead Section, § 5. Identity Over Time
69. • Jacquette 2014, pp. xi–xii
    • Sadegh-Zadeh 2011, p. 384
70. • Jacquette 2014, pp. xi–xii
    • Smith & Klagges 2008, p. 21
    • Sadegh-Zadeh 2011, p. 384
71. Jacquette 2014, pp. xii–xiii
72. • Epstein 2024, Lead Section
    • Tuomela, Hakli & Mäkelä 2020, § 1. Background to Social Ontology
73. • Ney 2014, pp. 259–263
    • Rea 2021, pp. 185–186
74. • Smith & Klagges 2008, p. 21
    • Hawley 2016, pp. 168–170
75. • Smith & Klagges 2008, pp. 35–36
    • Haritha et al. 2018, p. 489
76. • Hennig 2008, pp. 43–44
    • Hakkarainen & Keinänen 2023, pp. 1–2
    • Albertazzi 1996, p. 199
77. • Albertazzi 1996, pp. 199, 206
    • Hennig 2008, pp. 43–44
78. • Albertazzi 1996, pp. 199–200
    • Poli & Simons 1996, pp. vii–viii
    • Hakkarainen & Keinänen 2023, p. 9
79. Hakkarainen & Keinänen 2023, p. 9
80. • Berto & Plebani 2015, pp. 35–36
    • Phillips 1967, pp. 105–106
    • Haack 1979, pp. 361–362
81. • Coggins 2010, p. 93
    • Lehrer 1993, p. xi
82. • Berto & Plebani 2015, p. 2
    • Göhner & Steinbrink 2018, pp. 42, 52–53
83. • Wheeler 2020, § 2.2.1 The Question
    • Schalow 2019, p. 139
84. Niiniluoto 2002, pp. 1–2, 21, 25–26, 28–29
85. • Niiniluoto 2002, pp. 1–2, 21, 25–26
    • Chalmers 2009, pp. 77–78
    • Sider 2009, pp. 385–386
86. • Chalmers 2009, pp. 77–78
    • Sider 2009, pp. 385–386
87. • Chalmers 2009, p. 78
    • Hofweber 2023, § 4.4 Carnap’s rejection of ontology. (L1) meets (O4) and (the end of?) (O2)
88. Niiniluoto 2002, pp. 1–2, 21, 25–26, 28–29
89. • MacLeod & Rubenstein, Lead Section, § 2. Versions of Realism, § 3. Versions of Anti-Realism
    • Bigelow 1998a, § 4. Nominalism and Realism
    • Loux & Crisp 2017, pp. 17–19, 45
    • Niiniluoto 2002, pp. 28–29
90. • Blanchette 1998, Lead Section
    • Moore 1998, Lead Section
    • Balaguer 2009, p. 36
    • Linnebo 2024, Lead Section
91. • Balaguer 2009, pp. 36, 44
    • Weir 2024, Lead Section
92. • Borghini 2016, pp. 91–93
    • Chihara 2001, pp. 142–143
    • Parent, Lead section
93. Chakravartty 2017, § 1. What is Scientific Realism?
94. • Chakravartty 2017, Lead Section, § 1. What is Scientific Realism?
    • Liston, Lead Section, § 6b. The Observable-Unobservable Distinction
    • Okasha 2016, pp. 54–55
95. • DeLapp, Lead Section, § 4a. Moral Realisms, § 4b. Moral Relativisms
    • Sayre-McCord 2023a, Lead Section
    • Gowans 2021, Lead Section, § 2. Forms and Arguments
    • Westacott, Lead Section
    • Dreier 2007, pp. 240–241
96. • Van Inwagen 2011, pp. 389–390
    • Paul 2017, pp. 32–33
    • Woznicki 2022, p. 97
97. Van Inwagen 2011, pp. 389–390
98. • Van Inwagen 2011, pp. 389–390
    • Paul 2017, pp. 32–33
    • Woznicki 2022, p. 97
99. • Schaffer 2018, Lead Section
    • Robinson 2023, § Lead Section
100. • McLaughlin 1999, pp. 685–691
     • Kim 2005, p. 608
     • Sprigge 1998, Lead Section
101. • Stubenberg & Wishon 2023, Lead Section; § 1.3 Mind and Matter Revisited
     • Griffin 1998
102. • Calef, Lead Section
     • Robinson 2023, § Lead Section
103. Levine 2002, pp. 71–72, 84–85
104. Schaffer 2018, Lead Section
105. • Paul 2017, p. 34
     • Robinson & Weir 2024, § Lead section
     • O'Conaill 2022, pp. 1–3
106. • Paul 2017, pp. 34–35
     • Robinson & Weir 2024, § 3.2.2. The concept of substratum or 'thin particular'
107. • O'Conaill 2022, pp. 52–53
     • Robinson & Weir 2024, § Lead section
108. • O'Conaill 2022, p. 53
     • Esfeld 2020, pp. 464–465
109. Esfeld 2020, pp. 459–460
110. • O'Conaill 2022, p. 53
     • Robinson & Weir 2024, § Lead section
     • Rescher 2000, pp. 5–6
111. • Paul 2017, pp. 35–37
     • O'Conaill 2022, pp. 52–53
112. • Heil 2009, p. 310
     • Runggaldier 2009, p. 248
     • Lupisella 2020, p. 70
113. • Hoefer, Huggett & Read 2023, Lead Section
     • Benovsky 2016, pp. 19–20
     • Romero 2018, p. 135
114. • Esfeld 2020, pp. 461–462
     • Ladyman 2023, § 4. Ontic Structural Realism (OSR)
115. • Campbell 2006, p. 25, § States of affairs
     • Rosenkrantz 2018, pp. 1–4
     • Armstrong 2010, pp. 26–28
116. Wittgenstein 2001
117. • Thomasson 2022, § 1.1 Aristotelian Realism
     • Studtmann 2024, § 2. The Ten-Fold Division
     • Wardy 1998, § 1. Categories in Aristotle
118. • Westerhoff 2019, § Three important systems of categories: Vaiśeṣika
     • Kumar 2019, p. 34
119. • Thomasson 2022, § 1.2 Kantian Conceptualism
     • Wardy 1998, § 1. Categories in Kant
120. • Thomasson 2022, § 1.3 Husserlian Descriptivism, § 1.4 Contemporary Category Systems
     • Grim & Rescher 2023, p. 39
121. • Rea 2021, pp. 104–105
     • Heil 2009, p. 310
     • Runggaldier 2009, p. 248
     • Lupisella 2020, p. 70
122. • Rea 2021, pp. 104–105
     • Van Inwagen 2011, pp. 390–392
     • Koslicki 2018, p. 11
     • Rettler & Bailey 2023, § 3.2 What Objects Are
123. • Houng 2012, pp. 106–110
     • Schaffer 2009, pp. 347–348, 354–356
     • Ceder 2018, § Flat ontology
124. • Schaffer 2010, pp. 31, 44–45
     • Schaffer 2009, pp. 354–356
     • Ceder 2018, § Flat ontology
125. • Houng 2012, pp. 106–110
     • Schaffer 2009, pp. 347–348, 354–356
     • Ceder 2018, § Flat ontology
126. Houng 2012, pp. 106–110
127. • Miller 2018, Lead Section
     • Costa, Lead Section, § 1. Theories of Persistence
     • Simons 2013, p. 166
     • Hawley 2023, 3. Change and Temporal Parts
128. • Cisney, Lead Section
     • Rae 2020, p. 33
     • Rae 2014, p. 86
129. • Young 2021, pp. 83–84
     • Isrow 2022, p. 28
     • Neyrat 2020, p. 13
130. • Effingham 2013, § Methodology: Metaontology
     • Berto & Plebani 2015, p. 2
131. Thomasson 2012, pp. 175–176
132. • Garcia-Godinez 2023, pp. 189–192
     • Shaffer 2015, pp. 555–556
133. Garcia-Godinez 2023, pp. 186, 188–189
134. • Drummond 2022, p. 75
     • Ryckman 2005, pp. 142–144
135. Spear, § 3. Ideas Pertaining to a Pure Phenomenology and to a Phenomenological Philosophy: The Perceptual Noema
136. • Gabriel 2011, pp. ix–x
     • Körner 1984, pp. 183–184
     • Pihlström 2009, pp. 60–61
137. • Daly 2015, pp. 11–12
     • Berto & Plebani 2015, p. 35
138. • Goldenbaum, Lead Section, § 1. The Geometrical Method
     • Leuenberger 2017, p. 57
139. • Tahko 2015, pp. 177–178
     • Robinson 2004, pp. 537–538, 541–542
     • Brown & Fehige 2019, Lead Section
     • Goffi & Roux 2011, pp. 165, 168–169
140. Kirk 2023, Lead Section, § 2. Zombies and Physicalism
141. • Berto & Plebani 2015, p. 3
     • Ney 2014, pp. 30–31
     • Van Inwagen, Sullivan & Bernstein 2023, § 4. The Methodology of Metaphysics
142. • Ney 2014, pp. 40–41
     • Göhner & Steinbrink 2018, pp. 48
143. • Ney 2014, pp. 37–38, 40–43
     • Van Inwagen, Sullivan & Bernstein 2023, § 4. The Methodology of Metaphysics
     • Vineberg 2013, p. 133
144. • Effingham 2013, § Methodology: Theory choice
     • Göhner & Steinbrink 2018, pp. 57–58
145. • Ney 2014, pp. 48–49
     • Jacquette 2014, pp. 207–208
146. • Effingham 2013, § Methodology: Ontological parsimony
     • Brenner 2024, pp. 20–21
     • Göhner & Steinbrink 2018, p. 58
147. • Effingham 2013, § Methodology: Ontological parsimony
     • Göhner & Steinbrink 2018, p. 59
148. • Effingham 2013, § Methodology: Coherence with Intuitions
     • Berto & Plebani 2015, p. 35
149. • Grenon 2008, p. 70
     • Gómez-Pérez, Fernández-López & Corcho 2006, pp. v, 195
     • Fernández-López & Gómez-Pérez 2002, p. 129
150. • Kendall & McGuinness 2022, pp. 47–49
     • Gómez-Pérez, Fernández-López & Corcho 2006, pp. 109–110
151. • Gómez-Pérez, Fernández-López & Corcho 2006, pp. 153, 195
     • Babkin & Ulitin 2024, p. 28
     • Fernández-López & Gómez-Pérez 2002, p. 129
152. • Gómez-Pérez, Fernández-López & Corcho 2006, pp. 112–113
     • Fernández-López & Gómez-Pérez 2002, p. 129
153. Hofweber 2023, Lead Section, § 2.1 Different conceptions of logic
154. • Cook 2009, pp. 112–113
     • Casati & Fujikawa, Lead Section, §1. Existence as a Second-Order Property and Its Relation to Quantification
     • Albertazzi 1996, p. 206
155. Hofweber 2023, § 4.6 The form of thought and the structure of reality. (L4) meets (O3)
156. • Hofweber 2023, § 4.5 The fundamental language. (L1) meets (O4) and (the new beginning of?) (O2)
     • Hofweber 2021, p. 89
157. Heckmann 2006, p. 42
158. • Grütter & Bauer-Messmer 2007, p. 350
     • Hawley 2016, pp. 168–170
159. Kozierkiewicz & Pietranik 2019, p. 24
160. • Hameed, Preece & Sleeman 2013, pp. 231–233
     • Stuart 2016, p. 14
161. • Chicco & Masseroli 2018, pp. 832
     • Masseroli 2018, p. 814
162. Masseroli 2018, p. 814
163. Pouchard, Devarakon & Bransetter 2015, pp. 37–38
164. Yu 2014, pp. 357–359
165. Scott 2013, pp. 859–872
166. • Scott 2013, pp. 859–872
     • Heywood 2012, pp. 143–151
167. Ludwig & Weiskopf 2019
168. • Pack 2023, pp. 105–107, Animist Ontologies, Abstraction, and Slavery
     • Pack 2022, pp. 162–163
     • Sinclair 2022, p. 96, Righting Names: The Importance of Native American Philosophies of Naming for Environmental Justice
169. • Grayling 2019, Anselm
     • Dehsen 2013, p. 10
170. • Halteman 1998, Lead Section
     • Thomson 2011, p. 114
171. Ruzsa, § 1. History
172. • Baird 2017, p. 5
     • Grayling 2019, § Indian Philosophy
173. • Ruzsa, Lead Section
     • Grayling 2019, § Indian Philosophy
174. • Lopez 2010, p. 1426
     • Ruzsa, Lead Section
     • Grayling 2019, § Indian Philosophy
175. Lopez 2010, p. 1426
176. • Ambuel 1998, § 1. Categories
     • Lopez 2010, p. 1426
177. • Dynes 2016, p. 60
     • Littlejohn, § 2. Classical Sources for Our Understanding of Daoism
178. • Littlejohn, § 5. Fundamental Concepts in the Daodejing
     • Dynes 2016, pp. 60–61
179. • Chai 2020, p. 19
     • Robinet 2013, Chongxuan
180. • Graham, § 1. Presocratic Thought
     • Rée & Urmson 2004, pp. 308–309
181. • Kahn 2009, p. 143
     • Graham, § 6.a. Parmenides
182. • Hancock 2006, pp. 184–185
     • Hamlyn 2005, p. 590
     • Graham, § 3b. Metaphysics
183. • Thomasson 2022, § 1.1 Aristotelian Realism
     • Studtmann 2024, § 2. The Ten-Fold Division
     • Wardy 1998, § 1. Categories in Aristotle
184. • Halfwassen 2014, p. 185
     • Hancock 2006, pp. 187–188
     • Hamlyn 2005, pp. 590–591
     • Graham, § 5. Post-Hellenistic Thought
185. • Hancock 2006, pp. 188–189
     • Grayling 2019, § Boethius, § Abelard
     • Marenbon 2009, p. 6
     • Sweeney 2016, pp. 10–11
186. • Buren 2023, p. 53
     • Hancock 2006, p. 189
187. • Aertsen 2009, p. 117
     • Goris & Aertsen 2019, § 4.1 The first model: God as the cause of transcendental being (Thomas Aquinas)
     • Kuhlmann 2010, p. 1859
188. • Gilson 2018, § 1C Common Being, § 6C Unity of the Concrete
     • Williams 2022, § 2.3 Divine Infinity and the Doctrine of Univocity, § 3.3 Universals and Individuation
189. • Hancock 2006, p. 190
     • Grayling 2019, § Ockham
     • Kuhlmann 2010, p. 1859b
190. Thompson 2021, § 4. Natural Philosophy
191. Lizzini 2021, § 2.1 Ontology and Theology, § 2.4 Univocacy of Being and Ontological Distinction
192. • Grayling 2019, § Indian Philosophy
     • Perrett 2016, § The Medieval Period of Indian Philosophy
     • Dalal 2021, Lead Section, § 2.3 Two-Tiered Reality
193. • Ambuel 1998, § 10. Nonexistence or absence
     • Bhattacharya 2013, p. 35
194. • Berthrong, Lead Section, § 4. Traits, Themes and Motifs
     • Wu 2022, p. 56
     • Smart 2008, p. 99
195. • Hamlyn 2005, p. 591
     • Dehsen 2013, p. 51
196. • Hancock 2006, p. 190
     • Hamlyn 2005, p. 591
197. • Hancock 2006, pp. 190–191
     • Hamlyn 2005, p. 591
     • Look 2020, § 4. Metaphysics: A Primer on Substance
     • Menzel 2023, 1. Possible Worlds and Modal Logic
198. • Robinson & Weir 2024, § 2.5.1 Locke on 'pure substance in general'
     • Kuhlmann 2010, p. 1860b
199. • Svare 2006, p. 15
     • Hettche & Dyck 2019, § 5. Metaphysics
200. • Hancock 2006, p. 192
     • Hamlyn 2005, p. 591
201. • Lorini 2015, pp. 71, 75–76
     • Grier 2022, § 1. Preliminary Remarks: The Rejection of Ontology (general metaphysics) and the Transcendental Analytic
202. • Redding 2020, § 3.1.2 Science of Logic
     • Houlgate 2006, p. 117
203. • Grayling 2019, § Schopenhauer
     • Janaway 1999, pp. 248–249
204. • Hancock 2006, p. 193
     • Hamlyn 2005, p. 592
     • Grayling 2019, § Idealism
205. Johansson 2014, p. 226
206. Banhatti 1995, p. 151
207. • Vernekar 1998, pp. 81–86
     • Lawrence 2018, p. 415
     • Phillips 1998, Lead section, § Metaphysics
208. Boedeker 2008, p. 156
209. • Wheeler 2020, § 2.2.1 The Question
     • Schalow 2019, p. 139
210. Onof, Lead Section
211. • Poli 2011, pp. 1, 11, 21–22
     • Peterson & Poli 2022, § 3. What is the Relationship between Thinking and Being?, § 5.2 Strata
212. Aspenson 2016, § 1.4 Essential Terms of Metaphysics: Ontology
213. • Proops 2022, Lead Section
     • Klement 2019, Lead Section
     • Mumford 2003, p. 100
     • Loux & Crisp 2017, p. 148
214. • Desmet & Irvine 2022, § 6. Metaphysics
     • Palmer 1998, p. 175
215. • Chalmers 2009, p. 78
     • Hofweber 2023, § 4.4 Carnap’s rejection of ontology. (L1) meets (O4) and (the end of?) (O2)
216. • Ney 2014, pp. 37–38, 40
     • Van Inwagen, Sullivan & Bernstein 2023, § 4. The Methodology of Metaphysics
217. Parent, § 2. Lewis' Realism
218. • Guizzardi 2007, pp. 18–19
     • Sales & Guizzardi 2017, p. 28

Sources

• Aertsen, Jan A. (2009). "Aquinas, St. Thomas". In Kim, Jaekwon; Sosa, Ernest; Rosenkrantz, Gary S. (eds.). A Companion to Metaphysics. John Wiley & Sons. ISBN 978-1-4051-5298-3. Archived from the original on 2024-06-22. Retrieved 2024-06-26.
• Albertazzi, Liliana (1996). "Formal and Material Ontology". In Poli, Roberto; Simons, Peter (eds.). Formal Ontology. Nijhoff International Philosophy Series. Vol. 53. Springer Netherlands. pp. 199–232. doi:10.1007/978-94-015-8733-4_8. ISBN 978-94-015-8733-4. Archived from the original on 2024-06-18. Retrieved 2024-06-20.
• Ambuel, David (1998). "Ontology in Indian Philosophy". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-F063-1. ISBN 978-0-415-25069-6. Archived from the original on 25 June 2024. Retrieved 22 June 2024.
• Armstrong, D. M. (2010). Sketch for a Systematic Metaphysics. Oxford University Press. ISBN 978-0-19-161542-9. Archived from the original on 2024-06-08. Retrieved 2024-06-12.
• Aspenson, Steven Scott (2016). The Philosopher's Tool Kit. Routledge. ISBN 978-1-315-29291-5. Archived from the original on 2024-06-24. Retrieved 2024-06-26.
• Babkin, Eduard; Ulitin, Boris (2024). Ontology-Based Evolution of Domain-Oriented Languages: Models, Methods and Tools for User Interface Design in General-Purpose Software Systems. Springer Nature. ISBN 978-3-031-42202-7. Archived from the original on 2024-06-17. Retrieved 2024-06-17.
• Baird, Forrest (2017). Philosophic Classics: Asian Philosophy. Vol. 4. Routledge. ISBN 978-1-351-21745-3. Archived from the original on 2024-06-21. Retrieved 2024-06-26.
• Balaguer, Mark (2009). "Realism and Anti-Realism in Mathematics". Philosophy of Mathematics. Elsevier. ISBN 978-0-08-093058-9. Archived from the original on 2024-06-02. Retrieved 2024-06-12.
• Bangu, Sorin (2012). The Applicability of Mathematics in Science: Indispensability and Ontology. Palgrave Macmillan UK. ISBN 978-0-230-28520-0.
• Banhatti, G. S. (1995). Life and Philosophy of Swami Vivekananda. Atlantic Publishers & Dist. ISBN 978-81-7156-291-6.
• Benovsky, Jiri (2016). Meta-metaphysics: On Metaphysical Equivalence, Primitiveness, and Theory Choice. Springer. ISBN 978-3-319-25334-3. Archived from the original on 26 March 2024. Retrieved 29 March 2024.
• Berthrong, John H. "Neo-Confucian Philosophy". Internet Encyclopedia of Philosophy. Archived from the original on 6 February 2024. Retrieved 31 March 2024.
• Berto, Francesco; Jago, Mark (2023). "Impossible Worlds". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 10 February 2021. Retrieved 3 July 2024.
• Berto, Francesco; Plebani, Matteo (2015). Ontology and Metaontology: A Contemporary Guide. Bloomsbury Publishing. ISBN 978-1-4725-7330-8. Archived from the original on 30 August 2023. Retrieved 1 September 2023.
• Bhattacharya, Kamaleswar (2013). "On Two Questions of the New Logic of India". In Schumann, Andrew (ed.). Logic in Religious Discourse. Ontos Verlag. ISBN 978-3-11-031957-6. Archived from the original on 2024-06-25. Retrieved 2024-06-26.
• Bigelow, John C. (1998). "Particulars". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-N040-1. ISBN 978-0-415-25069-6. Archived from the original on 25 March 2024. Retrieved 24 March 2024.
• Bigelow, John C. (1998a). "Universals". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-N065-1. ISBN 978-0-415-25069-6. Archived from the original on 25 March 2024. Retrieved 25 March 2024.
• Lawrence, David Peter (2018). "Tantra and Kashmiri Śaivism". In Bilimoria, Puruṣottama; Rayner, Amy (eds.). History of Indian Philosophy. Routledge. ISBN 978-0-415-30976-9.
• Blanchette, Patricia A. (1998). "Realism in the Philosophy of Mathematics". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-Y066-1. ISBN 978-0-415-25069-6. Archived from the original on 24 February 2024. Retrieved 2 June 2024.
• Boedeker, Edgar C. (2008). "Phenomenology". In Dreyfus, Hubert L.; Wrathall, Mark A. (eds.). A Companion to Heidegger. John Wiley & Sons. ISBN 978-0-470-99724-6. Archived from the original on 2024-06-25. Retrieved 2024-06-26.
• Bogen, James (2005). "Relations". The Oxford Companion to Philosophy. Oxford University Press. ISBN 978-0-19-926479-7.
• Borghini, Andrea (2016). A Critical Introduction to the Metaphysics of Modality. Bloomsbury Publishing. ISBN 978-1-4725-2194-1. Archived from the original on 2024-06-02. Retrieved 2024-06-12.
• Brenner, Andrew (2015). "Mereological Nihilism and the Special Arrangement Question". Synthese. 192 (5): 1295–1314. doi:10.1007/s11229-014-0619-7.
• Brenner, Andrew (2024). Personal Ontology: Mystery and Its Consequences. Cambridge University Press. ISBN 978-1-009-36707-3. Archived from the original on 2024-06-16. Retrieved 2024-06-17.
• Brown, James Robert; Fehige, Yiftach (2019). "Thought Experiments". Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 21 November 2017. Retrieved 29 October 2021.
• Buren, Franziska van (2023). Aristotle and the Ontology of St. Bonaventure. Leuven University Press. ISBN 978-94-6270-356-8. Archived from the original on 2024-06-25. Retrieved 2024-06-26.
• Calef, Scott. "Dualism and Mind". Internet Encyclopedia of Philosophy. Archived from the original on 23 June 2024. Retrieved 9 June 2024.
• Campbell, Keith (2006). "Ontology". In Borchert, Donald M. (ed.). Encyclopedia of Philosophy. 7: Oakeshott – Presupposition (2 ed.). Thomson Gale, Macmillan Reference. ISBN 978-0-02-865787-5. Archived from the original on 29 January 2021. Retrieved 21 March 2024.
• Casati, Filippo; Fujikawa, Naoya. "Existence". Internet Encyclopedia of Philosophy. ISSN 2161-0002. Archived from the original on 10 August 2023. Retrieved 7 August 2023.
• Ceder, Simon (2018). "Framing Posthumanism". Towards a Posthuman Theory of Educational Relationality. Routledge. ISBN 978-1-351-04417-2. Archived from the original on 2024-06-08. Retrieved 2024-06-12.
• Ceylan, Yasin (1993). "A Critical Approach to the Avicennian Distinction of Essence and Existence". Islamic Studies. 32 (3): 329–337. ISSN 0578-8072. JSTOR 20840134. Archived from the original on 2023-08-11. Retrieved 2023-09-01.
• Chai, David (2020). Dao Companion to Xuanxue 玄學 (Neo-Daoism). Springer Nature. ISBN 978-3-030-49228-1. Archived from the original on 2 April 2024. Retrieved 4 April 2024.
• Chakravartty, Anjan (2017). "Scientific Realism". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 30 April 2019. Retrieved 2 June 2024.
• Chalmers, David (2009). "Ontological Anti-Realism". In Chalmers, David; Manley, David; Wasserman, Ryan (eds.). Metametaphysics: New Essays on the Foundations of Ontology. Oxford University Press. ISBN 978-0-19-954604-6.
• Chicco, David; Masseroli, Marco (2018). "Biological and Medical Ontologies: Protein Ontology (PRO)". Encyclopedia of Bioinformatics and Computational Biology: ABC of Bioinformatics. Elsevier. ISBN 978-0-12-811432-2. Archived from the original on 2024-06-28. Retrieved 2024-06-29.
• Chihara, Charles S. (2001). "Anti-Modal Realism". The Worlds of Possibility. Oxford University Press. pp. 142–181. doi:10.1093/acprof:oso/9780199246557.003.0005. ISBN 978-0-19-924655-7.
• Cisney, Vernon W. "Differential Ontology". Internet Encyclopedia of Philosophy. Archived from the original on 23 May 2024. Retrieved 10 June 2024.
• Coggins, Geraldine (2010). Could There Have Been Nothing?: Against Metaphysical Nihilism. Springer. ISBN 978-0-230-29524-7. Archived from the original on 2024-06-19. Retrieved 2024-06-20.
• Colyvan, Mark (2001). The Indispensability of Mathematics. Oxford University Press. ISBN 978-0-19-803144-4.
• Cook, Roy T. (2009). Dictionary of Philosophical Logic. Edinburgh University Press. ISBN 978-0-7486-3197-1. Archived from the original on 16 August 2023. Retrieved 1 September 2023.
• Cornell, David. "Material Composition". Internet Encyclopedia of Philosophy. Archived from the original on 25 March 2024. Retrieved 30 June 2024.
• Costa, Damiano. "Persistence in Time". Internet Encyclopedia of Philosophy. Archived from the original on 17 August 2021. Retrieved 26 March 2024.
• Cowling, Sam (2019). "Universals". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-N065-2. ISBN 978-0-415-25069-6. Archived from the original on 29 March 2024. Retrieved 25 March 2024.
• Craig, Edward (1998). "Ontology". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-N039-1. ISBN 978-0-415-25069-6. Archived from the original on 20 March 2024. Retrieved 17 June 2024.
• Craig, Edward (1998a). "Metaphysics". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-N095-1. ISBN 978-0-415-25069-6. Archived from the original on 1 August 2023. Retrieved 17 June 2024.
• Dalal, Neil (2021). "Śaṅkara". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 27 January 2022. Retrieved 2 April 2024.
• Daly, Chris (2009). "To Be". In Poidevin, Robin Le; Peter, Simons; Andrew, McGonigal; Cameron, Ross P. (eds.). The Routledge Companion to Metaphysics. Routledge. ISBN 978-1-134-15585-9. Archived from the original on 17 August 2023. Retrieved 1 September 2023.
• Daly, Christopher (2015). "Introduction and Historical Overview". The Palgrave Handbook of Philosophical Methods. Palgrave Macmillan UK. pp. 1–30. doi:10.1057/9781137344557_1. ISBN 978-1-137-34455-7. Archived from the original on 1 May 2022. Retrieved 18 April 2022.
• Dehsen, Christian von (2013). Philosophers and Religious Leaders. Routledge. ISBN 978-1-135-95102-3. Archived from the original on 28 May 2023. Retrieved 28 May 2023.
• DeLapp, Kevin M. "Metaethics". Internet Encyclopedia of Philosophy. Archived from the original on January 23, 2024. Retrieved 19 December 2023.
• Desmet, Ronald; Irvine, Andrew David (2022). "Alfred North Whitehead". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved 1 April 2024.
• Deutscher, Max (2021). Towards Continental Philosophy: Reason and Imagination in the Thought of Max Deutscher. Rowman & Littlefield. ISBN 978-1-5381-4777-1.
• Dreier, James (2007). "Moral Relativism and Moral Nihilism". In Copp, David (ed.). The Oxford Handbook of Ethical Theory. Oxford University Press. doi:10.1093/oxfordhb/9780195325911.003.0010. ISBN 978-0-19-989207-5.
• Drummond, John J. (2022). Historical Dictionary of Husserl's Philosophy. Rowman & Littlefield. ISBN 978-1-5381-3345-3. Archived from the original on 17 March 2024. Retrieved 18 March 2024.
• Dynes, Wayne R. (2016). "Creation of Daoism (6th Century BC)". In Curta, Florin; Holt, Andrew (eds.). Great Events in Religion: An Encyclopedia of Pivotal Events in Religious History. Bloomsbury Publishing USA. ISBN 978-1-61069-566-4. Archived from the original on 30 March 2024. Retrieved 4 April 2024.
• Effingham, Nikk (2013). Introduction to Ontology. Polity Press. ISBN 978-0-7456-5254-2.
• Epstein, Brian (2024). "Social Ontology". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved 18 June 2024.
• Esfeld, Michael (2020). "Thing and Non-Thing Ontologies". In Bliss, Ricki; Miller, J. T. M. (eds.). The Routledge Handbook of Metametaphysics. Taylor & Francis. ISBN 978-1-351-62250-9. Archived from the original on 2024-06-05. Retrieved 2024-06-12.
• Falguera, José L.; Martínez-Vidal, Concha; Rosen, Gideon (2022). "Abstract Objects". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 22 January 2021. Retrieved 12 August 2023.
• Faye, Jan (2013). "Is Time an Abstract Entity?". In Stadler, Friedrich; Stöltzner, Michael (eds.). Time and History: Proceedings of the 28. International Ludwig Wittgenstein Symposium, Kirchberg am Wechsel, Austria 2005. Walter de Gruyter. ISBN 978-3-11-033321-3. Archived from the original on 13 August 2023. Retrieved 1 September 2023.
• Fernández-López, Mariano; Gómez-Pérez, Asunción (2002). "Overview and Analysis of Methodologies for Building Ontologies". The Knowledge Engineering Review. 17 (2): 129–156. doi:10.1017/S0269888902000462.
• Fine, Kit (1995). "Ontological Dependence". Proceedings of the Aristotelian Society. 95 (1): 269–290. doi:10.1093/aristotelian/95.1.269.
• Gabriel, Markus (2011). Transcendental Ontology: Essays in German Idealism. Continuum. ISBN 978-1-4411-1629-1. Archived from the original on 2024-06-16. Retrieved 2024-06-17.
• Gallois, Andre (2016). "Identity Over Time". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved 28 March 2024.
• Garcia-Godinez, Miguel (2023). "Easy Social Ontology". In Garcia-Godinez, Miguel (ed.). Thomasson on Ontology. Springer Nature. ISBN 978-3-031-23672-3. Archived from the original on 2024-06-13. Retrieved 2024-06-17.
• Gibson, Q. B. (1998). The Existence Principle. Springer Science & Business Media. ISBN 978-0-7923-5188-7. Archived from the original on 10 August 2023. Retrieved 1 September 2023.
• Gilson, Etienne (2018). John Duns Scotus: Introduction to His Fundamental Positions. Bloomsbury. ISBN 978-0-567-67870-6. Archived from the original on 2024-07-06. Retrieved 2024-06-26.
• Goffi, J.-Y.; Roux, S. (2011). "On The Very Idea Of A Thought Experiment". Thought Experiments in Methodological and Historical Contexts (PDF). Brill. pp. 165–191. doi:10.1163/ej.9789004201767.i-233.35. ISBN 978-90-04-20177-4.
• Göhner, Julia Friederike; Steinbrink, Lukas (2018). "Ontological Commitments, Ordinary Language, and Theory Choice". In Jansen, Ludger; Näger, Paul M. (eds.). Peter van Inwagen: Materialism, Free Will and God. Springer. ISBN 978-3-319-70052-6. Archived from the original on 2024-06-16. Retrieved 2024-06-17.
• Goldenbaum, Ursula. "Geometrical Method". Internet Encyclopedia of Philosophy. Archived from the original on 7 March 2022. Retrieved 15 March 2024.
• Gómez-Pérez, Asunción; Fernández-López, Mariano; Corcho, Oscar (2006). Ontological Engineering: With Examples from the Areas of Knowledge Management, e-Commerce and the Semantic Web (1 ed.). Springer Science & Business Media. ISBN 978-1-85233-840-4. Archived from the original on 2024-06-16. Retrieved 2024-06-17.
• Goris, Wouter; Aertsen, Jan (2019). "Medieval Theories of Transcendentals". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 6 July 2024. Retrieved 22 June 2024.
• Gowans, Chris (2021). "Moral Relativism". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on February 1, 2024. Retrieved 19 December 2023.
• Graham, Jacob. "Presocratics". Internet Encyclopedia of Philosophy. Archived from the original on 9 February 2021. Retrieved 21 June 2024.
• Grayling, A. C. (2019). The History of Philosophy. Penguin UK. ISBN 978-0-241-98086-6. Archived from the original on 3 July 2023. Retrieved 30 June 2023.
• Grenon, Pierre (2008). "A Primer on Knowledge Management and Ontological Engineering". In Munn, Katherine; Smith, Barry (eds.). Applied Ontology: An Introduction. Ontos Verlag. ISBN 978-3-938793-98-5.
• Grier, Michelle (2022). "Kant's Critique of Metaphysics". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 6 July 2024. Retrieved 25 June 2024.
• Griffin, Nicholas (1998). "Neutral Monism". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-N035-1. ISBN 978-0-415-25069-6. Archived from the original on 27 March 2024. Retrieved 27 March 2024.
• Grim, Patrick; Rescher, Nicholas (2023). Theory of Categories: Key Instruments of Human Understanding. Anthem Press. ISBN 978-1-83998-815-8. Archived from the original on 23 March 2024. Retrieved 29 March 2024.
• Grove, Richard W.; Short, Edmund C. (1991). "Theoretical Inquiry: Components and Structure". In Short, Edmund C. (ed.). Forms of Curriculum Inquiry. SUNY Press. ISBN 978-0-7914-0649-6.
• Grütter, Rolf; Bauer-Messmer, Bettina (2007). "Towards Spatial Reasoning in the Semantic Web: A Hybrid Knowledge Representation System Architecture". In Fabrikant, Sara; Wachowicz, Monica (eds.). The European Information Society: Leading the Way with Geo-information. Springer. ISBN 978-3-540-72385-1.
• Guizzardi, Giancarlo (2007). "On Ontology, Ontologies, Conceptualizations, Modeling Languages, and (Meta)Models". In Vasilecas, Olegas; Eder, Johann; Caplinskas, Albertas (eds.). Databases and Information Systems IV: Selected Papers from the Seventh International Baltic Conference, DB&IS'2006. IOS Press. ISBN 978-1-58603-715-4. Archived from the original on 2024-06-26. Retrieved 2024-06-26.
• Haack, Susan (1979). "Descriptive and Revisionary Metaphysics". Philosophical Studies. 35 (4): 361–371. doi:10.1007/bf00368051.
• Hakkarainen, Jani; Keinänen, Markku (2023). Formal Ontology. Cambridge University Press. ISBN 978-1-009-08033-0. Archived from the original on 2024-06-19. Retrieved 2024-06-20.
• Halfwassen, Jens (2014). "The Metaphysics of the One". In Slaveva-Griffin, Svetla; Remes, Pauliina (eds.). The Routledge Handbook of Neoplatonism. Routledge. ISBN 978-1-317-59136-8. Archived from the original on 2024-07-06. Retrieved 2024-06-26.
• Halteman, Matthew C. (1998). "Ontotheology". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-K115-1. ISBN 978-0-415-25069-6. Archived from the original on 28 June 2024. Retrieved 28 June 2024.
• Hameed, Adil; Preece, Alun; Sleeman, Derek (2013). "Ontology Reconciliation". In Staab, Steffen; Studer, Rudi (eds.). Handbook on Ontologies. Springer. ISBN 978-3-540-24750-0.
• Hamlyn, D. W. (2005). "Metaphysics, History of". The Oxford Companion to Philosophy. Oxford University Press. ISBN 978-0-19-926479-7. Archived from the original on 2024-07-06. Retrieved 2024-06-26.
• Hancock, Roger (2006). "Metaphysics, History of". In Borchert, Donald M. (ed.). The Encyclopedia of Philosophy. 6: Masaryk – Nussbaum (2 ed.). Thomson Gale, Macmillan Reference. ISBN 978-0-02-865786-8.
• Haritha, P.; Priyatharshini, R.; Abishek, A. G.; Kiran, V. Kamala (2018). "Knowledge Based Framework for Genetic Disease Diagnosis Using Data Mining Technique". In Uden, Lorna; Hadzima, Branislav; Ting, I.-Hsien (eds.). Knowledge Management in Organizations: 13th International Conference, KMO 2018, Žilina, Slovakia, August 6–10, 2018, Proceedings. Springer. ISBN 978-3-319-95204-8. Archived from the original on 2024-06-18. Retrieved 2024-06-20.
• Hartmann, Nicolai (2012). New Ways of Ontology. Transaction Publishers. ISBN 978-1-4128-4704-9. Archived from the original on 2024-07-06. Retrieved 2024-07-03.
• Hawley, Katherine (2016). "Applied Metaphysics". In Lippert-Rasmussen, Kasper; Brownlee, Kimberley; Coady, David (eds.). A Companion to Applied Philosophy. John Wiley & Sons. ISBN 978-1-118-86911-6.
• Hawley, Katherine (2023). "Temporal Parts". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 6 July 2024. Retrieved 26 March 2024.
• Heckmann, Dominikus (2006). Ubiquitous User Modeling. IOS Press. ISBN 978-3-89838-297-7.
• Heil, John (2009). "Relations". In Le Poidevin, Robin; Peter, Simons; Andrew, McGonigal; Cameron, Ross P. (eds.). The Routledge Companion to Metaphysics. Routledge. pp. 310–321. doi:10.4324/9780203879306-34. ISBN 978-0-203-87930-6.
• Hennig, Boris (2008). "What Is Formal Ontology?". In Munn, Katherine; Smith, Barry (eds.). Applied Ontology: An Introduction. Ontos Verlag. ISBN 978-3-938793-98-5.
• Hettche, Matt; Dyck, Corey (2019). "Christian Wolff". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 8 August 2019. Retrieved 2 April 2024.
• Heywood, Paolo (2012). "Anthropology and What There Is: Reflections on 'Ontology'". The Cambridge Journal of Anthropology. 30 (1): 143–151. doi:10.3167/ca.2012.300112. ISSN 0305-7674. JSTOR 43610895. Archived from the original on 2022-09-24. Retrieved 2022-09-24.
• Hoad, T. F. (1993). The Concise Oxford Dictionary of English Etymology. Oxford University Press. ISBN 978-0-19-283098-2.
• Hoefer, Carl; Huggett, Nick; Read, James (2023). "Absolute and Relational Space and Motion: Classical Theories". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved 26 March 2024.
• Hoffman, Joshua; Rosenkrantz, Gary S. (2008). The Divine Attributes. Blackwell. ISBN 978-0-470-69271-4.
• Hofweber, Thomas (2021). "Why Our Natural Languages are Ideal Languages for Metaphysics". In Miller, J. T. M. (ed.). The Language of Ontology. Oxford University Press. ISBN 978-0-19-264853-2. Archived from the original on 2024-06-28. Retrieved 2024-06-29.
• Hofweber, Thomas (2023). "Logic and Ontology". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 7 December 2021. Retrieved 31 May 2024.
• Houlgate, Stephen (2006). The Opening of Hegel's Logic: From Being to Infinity. Purdue University Press. ISBN 978-1-55753-256-5. Archived from the original on 2024-06-24. Retrieved 2024-06-26.
• Houng, Yu-Houng (2012). "Elminative Materialism and Connectionism". In Lin, Cheng-Hun; Fu, Daiwie (eds.). Philosophy and Conceptual History of Science in Taiwan. Springer Science & Business Media. ISBN 978-94-011-2500-0. Archived from the original on 2024-06-08. Retrieved 2024-06-12.
• Isrow, Zachary (2022). The Spectricity of Humanness: Spectral Ontology and Being-in-the-World. Walter de Gruyter. ISBN 978-3-11-069099-6. Archived from the original on 2024-06-10. Retrieved 2024-06-12.
• Jacob, Pierre (2023). "Intentionality". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on August 29, 2018. Retrieved 28 April 2024.
• Jacquette, Dale (2014). Ontology. Routledge. ISBN 978-1-317-48959-7. Archived from the original on 2024-06-16. Retrieved 2024-06-17.
• Janaway, Christopher (1999). "10. The Primacy of Will". Self and World in Schopenhauer's Philosophy. Oxford University Press. ISBN 978-0-19-825003-6. Archived from the original on 2 April 2024. Retrieved 4 April 2024.
• Jaroszyński, Piotr (2018). Metaphysics or Ontology?. Brill Rodopi. ISBN 978-90-04-35825-6.
• Jaroszyński, Piotr (2023). Culture: A Drama of Nature and Person. Brill. ISBN 978-90-04-69118-6. Archived from the original on 2024-07-06. Retrieved 2024-07-04.
• Johansson, Ingvar (2014). "All Relations are Internal: The New Version". In Reboul, Anne (ed.). Mind, Values, and Metaphysics: Philosophical Essays in Honor of Kevin Mulligan. Vol. 1. Springer. ISBN 978-3-319-04199-5. Archived from the original on 2024-06-25. Retrieved 2024-06-26.
• Jubien, Michael (1998). "Ontological Commitment". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-X027-1. ISBN 978-0-415-25069-6. Archived from the original on 23 February 2024. Retrieved 3 July 2024.
• Kahn, Charles H. (2009). Essays on Being. Oxford University Press. ISBN 978-0-19-156006-4. Archived from the original on 2024-07-06. Retrieved 2024-06-26.
• Kendall, Elisa F.; McGuinness, Deborah L. (2022). Ontology Engineering. Springer Nature. ISBN 978-3-031-79486-5. Archived from the original on 2024-07-06. Retrieved 2024-06-17.
• Kim, Jaegwon (2005). "Mind, Problems of the Philosophy of". The Oxford Companion to Philosophy. Oxford University Press. ISBN 978-0-19-926479-7. Archived from the original on 11 April 2024. Retrieved 29 March 2024.
• Kirk, Robert (2023). "Zombies". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 28 September 2020. Retrieved 15 March 2024.
• Kirwan, Christopher (2005). "Identity". The Oxford Companion to Philosophy. Oxford University Press. ISBN 978-0-19-926479-7. Archived from the original on 11 April 2024. Retrieved 29 March 2024.
• Klement, Kevin (2019). "Russell's Logical Atomism". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 11 April 2024. Retrieved 2 April 2024.
• Koons, Robert C.; Pickavance, Timothy H. (2015). Metaphysics: The Fundamentals (1 ed.). Wiley-Blackwell. ISBN 978-1-4051-9574-4.
• Korman, Daniel Z. (2021). "Material Constitution". Oxford Bibliographies Online. Oxford University Press. doi:10.1093/OBO/9780195396577-0386. ISBN 978-0-19-539657-7. Archived from the original on 6 July 2024. Retrieved 3 July 2024.
• Körner, Stephan (1984). Metaphysics: Its Structure and Function. Cambridge University Press. ISBN 978-0-521-26496-9. Archived from the original on 17 March 2024. Retrieved 18 March 2024.
• Koslicki, Kathrin (2018). Form, Matter, Substance. Oxford University Press. ISBN 978-0-19-255708-7. Archived from the original on 2024-07-06. Retrieved 2024-06-12.
• Kozierkiewicz, Adrianna; Pietranik, Marcin (2019). "A Formal Framework for the Ontology Evolution". In Nguyen, Ngoc Thanh; Gaol, Ford Lumban; Hong, Tzung-Pei; Trawiński, Bogdan (eds.). Intelligent Information and Database Systems: 11th Asian Conference, ACIIDS 2019, Yogyakarta, Indonesia, April 8–11, 2019, Proceedings, Part I. Springer. ISBN 978-3-030-14799-0.
• Kriegel, Uriah (2007). "Intentional Inexistence and Phenomenal Intentionality". Philosophical Perspectives. 21 (1): 307–340. doi:10.1111/j.1520-8583.2007.00129.x. ISSN 1520-8583.
• Kroon, Fred; Voltolini, Alberto (2023). "Fictional Entities". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on June 17, 2024. Retrieved 28 April 2024.
• Kuhlmann, Meinard (2010). "Ontologie". In Sandkühler, Hans Jörg (ed.). Enzyklopädie Philosophie (2 ed.). Meiner. ISBN 978-3-7873-1999-2.
• Kuhn, Thomas S. (2010). "Possible Worlds in History of Science". In Sture, Allén (ed.). Possible Worlds in Humanities, Arts and Sciences: Proceedings of Nobel Symposium 65. Walter de Gruyter. ISBN 978-3-11-086685-8. Archived from the original on 28 March 2024. Retrieved 29 March 2024.
• Kumar, ShashiPrabha (2019). Categories, Creation and Cognition in Vaiśeṣika Philosophy. Springer. ISBN 978-981-13-2965-4. Archived from the original on 2024-06-08. Retrieved 2024-06-12.
• Ladyman, James (2023). "Structural Realism". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 11 September 2019. Retrieved 5 June 2024.
• Lamarque, Peter (1998). "Fictional Entities". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-M021-1. ISBN 978-0-415-25069-6. Archived from the original on April 28, 2024. Retrieved 24 March 2024.
• LaZella, Andrew T. (2019). The Singular Voice of Being: John Duns Scotus and Ultimate Difference. Fordham University Press. ISBN 978-0-8232-8459-7. Archived from the original on 2024-07-06. Retrieved 2024-07-03.
• Lehrer, Keith (1993). "Preface". In Lehrer, Keith (ed.). Haecceity: An Ontological Essay. Springer Science & Business Media. ISBN 978-0-7923-2438-6. Archived from the original on 2024-06-19. Retrieved 2024-06-20.
• Leuenberger, Stephan (2017). "Wolff's Close Shafe with Fatalism". In Sinclair, Mark (ed.). The Actual and the Possible: Modality and Metaphysics in Modern Philosophy. Oxford University Press. ISBN 978-0-19-108973-2. Archived from the original on 2024-06-16. Retrieved 2024-06-17.
• Levine, Michael P. (2002). Pantheism: A Non-Theistic Concept of Deity. Routledge. ISBN 978-1-134-91157-8. Archived from the original on 2024-06-11. Retrieved 2024-06-12.
• Linnebo, Øystein (2024). "Platonism in the Philosophy of Mathematics". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 25 November 2018. Retrieved 2 June 2024.
• Liston, Michael. "Scientific Realism and Antirealism". Internet Encyclopedia of Philosophy. Archived from the original on 14 March 2024. Retrieved 2 June 2024.
• Littlejohn, Ronnie. "Daoist Philosophy". Internet Encyclopedia of Philosophy. Archived from the original on 29 March 2024. Retrieved 30 March 2024.
• Lizzini, Olga (2021). "Ibn Sina's Metaphysics". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 11 April 2024. Retrieved 23 June 2024.
• Look, Brandon C. (2020). "Gottfried Wilhelm Leibniz". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 5 August 2020. Retrieved 2 April 2024.
• Lopez, Carlos (2010). "India, Hinduism in: Medieval Period". In Melton, J. Gordon; Baumann, Martin (eds.). Religions of the World: A Comprehensive Encyclopedia of Beliefs and Practices. Bloomsbury. ISBN 978-1-59884-204-3. Archived from the original on 2024-07-06. Retrieved 2024-06-26.
• Lorini, Gualtiero (2015). "Kant's Metaphor by Analogy Between Ontology and Transcendental Philosophy". In Kauark-Leite, Patricia; Cecchinato, Giorgia; Figueiredo, Virginia De Araujo; Ruffing, Margit; Serra, Alice (eds.). Kant and the Metaphors of Reason. Georg Olms Verlag. ISBN 978-3-487-15124-3. Archived from the original on 2024-06-23. Retrieved 2024-06-26.
• Loux, Michael J.; Crisp, Thomas M. (2017). Metaphysics: A Contemporary Introduction (4 ed.). Routledge. ISBN 978-1-138-63933-1.
• Lowe, E. J. (2005). "Ontology". The Oxford Companion to Philosophy. Oxford University Press. ISBN 978-0-19-926479-7.
• Lowe, E. J. (2005a). "Being". The Oxford Companion to Philosophy. Oxford University Press. ISBN 978-0-19-926479-7. Archived from the original on 2024-07-06. Retrieved 2024-06-18.
• Lowe, E. J. (2005b). "Existence". The Oxford Companion to Philosophy. Oxford University Press. ISBN 978-0-19-926479-7. Archived from the original on 2024-07-06. Retrieved 2024-06-18.
• Lowe, E. J. (2006). The Four-Category Ontology: A Metaphysical Foundation for Natural Science. Clarendon Press. ISBN 978-0-19-925439-2.
• Ludwig, David; Weiskopf, Daniel A. (2019). "Ethnoontology: Ways of World-building Across Cultures". Philosophy Compass. 14 (9). doi:10.1111/phc3.12621. S2CID 199516840. Consider the animism debate. Animists consider nonhuman entities (e.g., plants, forests, or rivers) as intentional actors (Harvey, 2005). There is substantial evidence that animism is a widespread metaphysical view. For example, the Nayaka people of South India consider not only certain animals but also stones, hills, cups, and knives to be devaru: beings that stand in active, quasi-social relationships with them (Bird-David, 1999). Devaru are aspects of a larger kin structure that incorporates potential "partners" in the nonhuman world. In addition to these ethnographic observations, there are intriguing cross-cultural similarities in animist ontologies. Indigenous communities around the world tend to be much more permissive in their ascription of intentionality than Western participants (Ojalehto, Douglas, & García, 2017).
• Lupisella, Mark (2020). Cosmological Theories of Value: Science, Philosophy, and Meaning in Cosmic Evolution. Springer Nature. ISBN 978-3-030-25339-4. Archived from the original on 5 June 2024. Retrieved 12 June 2024.
• MacBride, Fraser (2020). "Relations". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 6 July 2024. Retrieved 2 July 2024.
• MacIntyre, Alasdair (2006). "Being". In Borchert, Donald M. (ed.). Encyclopedia of Philosophy. Vol. 1 (2 ed.). Macmillan Reference USA. ISBN 978-0-02-865781-3.
• Mackie, Penelope (1998). "Existence". Routledge Encyclopedia of Philosophy. Routledge. ISSN 2161-0002. Archived from the original on 10 August 2023. Retrieved 7 August 2023.
• Mackie, Penelope (2005). "Events". The Oxford Companion to Philosophy. Oxford University Press. ISBN 978-0-19-926479-7. Archived from the original on 2024-07-06. Retrieved 2024-06-18.
• MacLeod, Mary C.; Rubenstein, Eric M. "Universals". Internet Encyclopedia of Philosophy. Archived from the original on 24 February 2024. Retrieved 24 March 2024.
• Marenbon, John (2009). "Introduction: Reading Boethius Whole". In Marenbon, John (ed.). The Cambridge Companion to Boethius. Cambridge University Press. ISBN 978-1-139-82815-4. Archived from the original on 2 April 2024. Retrieved 4 April 2024.
• Marshall, Dan; Weatherson, Brian (2023). "Intrinsic Vs. Extrinsic Properties". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 6 July 2024. Retrieved 2 July 2024.
• Masseroli, Marco (2018). "Biological and Medical Ontologies: Introduction". Encyclopedia of Bioinformatics and Computational Biology: ABC of Bioinformatics. Elsevier. ISBN 978-0-12-811432-2. Archived from the original on 2024-06-28. Retrieved 2024-06-29.
• Maurin, Anna-Sofia (2019). "Particulars". Routledge Encyclopedia of Philosophy. Routledge Encyclopedia of Philosophy. doi:10.4324/9780415249126-N040-2. ISBN 978-0-415-25069-6. Archived from the original on 25 March 2024. Retrieved 29 March 2024.
• McLaughlin, Brian P. (1999). Audi, Robert (ed.). The Cambridge Dictionary of Philosophy (2 ed.). Cambridge University Press. ISBN 978-0-521-63722-0.
• Menzel, Christopher (2023). "Possible Worlds". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 6 July 2024. Retrieved 24 March 2024.
• Merriam-Webster (2024). "Definition of Ontology". Merriam-Webster Dictionary. Merriam-Webster. Archived from the original on 6 July 2018. Retrieved 17 June 2024.
• Miller, Kristie (2018). "Persistence". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/0123456789-N126-1. ISBN 978-0-415-25069-6. Archived from the original on 26 March 2024. Retrieved 26 March 2024.
• Moore, A. W. (1998). "Antirealism in the Philosophy of Mathematics". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-Y065-1. ISBN 978-0-415-25069-6. Archived from the original on 1 June 2024. Retrieved 2 June 2024.
• Mulligan, Kevin (2012). "Preface". In Mulligan, Kevin (ed.). Language, Truth and Ontology. Springer Science & Business Media. ISBN 978-94-011-2602-1. Archived from the original on 2024-06-17. Retrieved 2024-06-18.
• Mumford, Stephen, ed. (2003). "11. The Philosophy of Logical Atomism". Russell on Metaphysics: Selections from the Writings of Bertrand Russell. Routledge. ISBN 978-1-136-90272-7. Archived from the original on 2 April 2024. Retrieved 4 April 2024.
• Mumford, Stephen (2012). Metaphysics: A Very Short Introduction (1 ed.). Oxford University Press. ISBN 978-0-19-965712-4.
• Nelson, Michael (2022). "Existence". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 3 September 2018. Retrieved 6 August 2023.
• Ney, Alyssa (2014). Metaphysics: An Introduction. Routledge, Taylor & Francis Group. ISBN 978-0-415-64074-9.
• Neyrat, Frederic (2020). Literature and Materialisms. Routledge. ISBN 978-1-317-19845-1.
• Niiniluoto, Ilkka (2002). Critical Scientific Realism. Oxford University Press. ISBN 978-0-19-159809-8.
• Noonan, Harold; Curtis, Ben (2022). "Identity". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 23 July 2020. Retrieved 28 March 2024.
• Nuñez Erices, Gonzalo (2019). "Boundaries and Things. A Metaphysical Study of the Brentano-Chisholm Theory". KRITERION – Journal of Philosophy. 33 (2): 15–48. doi:10.1515/krt-2019-330203.
• O'Conaill, Donnchadh (2022). Substance. Cambridge University press. ISBN 978-1-108-94074-0.
• Okasha, Samir (2016). Philosophy of Science: A Very Short Introduction. Oxford University Press. ISBN 978-0-19-874558-7. Archived from the original on 2024-06-02. Retrieved 2024-06-12.
• Oliver, Alexander D. (2005). "Abstract Entities". The Oxford Companion to Philosophy. Oxford University Press. ISBN 978-0-19-926479-7. Archived from the original on 2024-07-06. Retrieved 2024-06-18.
• Onof, Christian J. "Sartre, Jean Paul: Existentialism". Internet Encyclopedia of Philosophy. Archived from the original on 26 June 2024. Retrieved 25 June 2024.
• Orilia, Francesco; Paolini Paoletti, Michele (2022). "Properties". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 16 April 2024. Retrieved 2 July 2024.
• O’Madagain, Cathal. "Intentionality". Internet Encyclopedia of Philosophy. ISSN 2161-0002. Archived from the original on April 28, 2024. Retrieved 28 April 2024.
• Pack, Justin (2022). Environmental Philosophy in Desperate Times. Broadview Press. pp. 162–163. ISBN 978-1-77048-866-3. Archived from the original on 2024-06-17. Retrieved 2024-05-05.
• Pack, Justin (2023). "Animist Ontologies, Abstraction, and Slavery". Money and Thoughtlessness: A Genealogy and Defense of the Traditional Suspicions of Money and Merchants. Springer Nature. pp. 105–107. ISBN 978-3-031-22261-0. Archived from the original on 2024-05-05. Retrieved 2024-05-05.
• Palmer, Clare (1998). Environmental Ethics and Process Thinking. Clarendon Press. ISBN 978-0-19-826952-6. Archived from the original on 2 April 2024. Retrieved 4 April 2024.
• Parent, Ted. "Modal Metaphysics". Internet Encyclopedia of Philosophy. Archived from the original on 11 November 2020. Retrieved 22 March 2024.
• Paul, L. A. (2017). "A One Category Ontology". In Keller, John A. (ed.). Being, Freedom, and Method: Themes from the Philosophy of Peter Van Inwagen. Oxford University Press. ISBN 978-0-19-871570-2.
• Pavel, Thomas G. (1986). Fictional Worlds. Harvard University Press. ISBN 978-0-674-29966-5. Archived from the original on 2024-02-17. Retrieved 2024-02-18.
• Perrett, Roy W. (2016). An Introduction to Indian Philosophy. Cambridge University Press. ISBN 978-0-521-85356-9. Archived from the original on 9 June 2023. Retrieved 4 April 2024.
• Peterson, Keith; Poli, Roberto (2022). "Nicolai Hartmann". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 6 July 2024. Retrieved 25 June 2024.
• Phillips, R. L. (1967). "Descriptive Versus Revisionary Metaphysics and the Mind–Body Problem". Philosophy. 42 (160): 105–118. doi:10.1017/S0031819100001030.
• Phillips, Stephen H. (1998). "Aurobindo Ghose (1872–1950)". Routledge Encyclopedia of Philosophy. Routledge. doi:10.4324/9780415249126-F076-1. ISBN 978-0-415-25069-6. Retrieved 24 October 2024. {{cite book}}: |website= ignored (help)
• Pihlström, Sami (2009). Pragmatist Metaphysics: An Essay on the Ethical Grounds of Ontology. A&C Black. ISBN 978-1-84706-593-3. Archived from the original on 17 March 2024. Retrieved 18 March 2024.
• Plebani, Matteo (2013). "Introduction". In Camposampiero, Favaretti Matteo; Plebani, Matteo (eds.). Existence and Nature: New Perspectives. Walter de Gruyter. ISBN 978-3-11-032180-7. Archived from the original on 20 August 2023. Retrieved 1 September 2023.
• Poli, Roberto (2011). "Hartmann's Theory of Categories: Introductory Remarks". In Poli, Roberto; Scognamiglio, Carlo; Tremblay, Frederic (eds.). The Philosophy of Nicolai Hartmann. Walter de Gruyter. ISBN 978-3-11-025418-1.
• Poli, Roberto; Simons, Peter (1996). "Foreword". In Poli, Roberto; Simons, Peter (eds.). Formal Ontology. doi:10.1007/978-94-015-8733-4. ISBN 978-0-7923-4104-8.
• Pouchard, Line; Devarakon, Ranjeet; Bransetter, Marcia (2015). "A Linked Science Investigation: Enhancing Climate Change Data Discovery with Ontologies and Semantic Technologies". In Narock, T.; Fox, P. (eds.). The Semantic Web in Earth and Space Science. Current Status and Future Directions. IOS Press. ISBN 978-1-61499-501-2. Archived from the original on 2024-07-04. Retrieved 2024-06-29.
• Prior, A. N. (2006). "Existence". In Borchert, Donald (ed.). Encyclopedia of Philosophy. Vol. 3 (2nd ed.). Macmillan Reference USA. ISBN 978-0-02-865790-5.
• Proops, Ian (2022). "Wittgenstein's Logical Atomism". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 6 July 2024. Retrieved 2 April 2024.
• Pruss, Alexander R.; Rasmussen, Joshua L. (2018). Necessary Existence. Oxford University Press. ISBN 978-0-19-874689-8. Archived from the original on 2023-08-18. Retrieved 2023-09-01.
• Rae, Gavin (2014). "Traces of Identity In Deleuze's Differential Ontology". International Journal of Philosophical Studies. 22 (1): 86–105. doi:10.1080/09672559.2013.861003.
• Rae, Gavin (2020). "Deleuze, Differential Ontology and Subjectivity". Poststructuralist Agency: The Subject in Twentieth-Century Theory. Edinburgh University Press. ISBN 978-1-4744-5938-9. Archived from the original on 2024-07-06. Retrieved 2024-06-12.
• Rea, Michael Cannon (1997). "Introduction". In Rea, Michael Cannon (ed.). Material Constitution: A Reader. Rowman & Littlefield. ISBN 978-0-8476-8384-0. Archived from the original on 2024-07-06. Retrieved 2024-07-03.
• Rea, Michael C. (2021). Metaphysics: The Basics (2 ed.). Routledge. ISBN 978-0-367-13607-9.
• Redding, Paul (2020). "Georg Wilhelm Friedrich Hegel". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 30 April 2019. Retrieved 24 June 2024.
• Rée, Jonathan; Urmson, J. O. (2004). The Concise Encyclopedia of Western Philosophy. Routledge. ISBN 978-1-134-33177-2. Archived from the original on 22 June 2023. Retrieved 16 June 2023.
• Reicher, Maria (2022). "Nonexistent Objects". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 1 February 2024. Retrieved 10 August 2023.
• Rescher, Nicholas (2000). Process Philosophy: A Survey of Basic Issues. University of Pittsburgh Press. ISBN 978-0-8229-7393-5. Archived from the original on 2024-06-05. Retrieved 2024-06-12.
• Rettler, Bradley; Bailey, Andrew M. (2023). "Object". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 16 June 2022. Retrieved 9 June 2024.
• Robinet, Isabelle (2013). "Chongxuan". In Pregadio, Fabrizio (ed.). The Encyclopedia of Taoism. Routledge. ISBN 978-1-135-79634-1. Archived from the original on 2 April 2024. Retrieved 4 April 2024.
• Robinson, Howard (2004). "Thought Experiments, Ontology, and Concept-Dependent Truthmakers". Monist. 87 (4): 537–553. doi:10.5840/monist200487422.
• Robinson, Howard (2023). "Dualism". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 7 November 2023. Retrieved 9 June 2024.
• Robinson, Howard; Weir, Ralph (2024). "Substance". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved 5 June 2024.
• Romero, Gustavo E. (2018). Scientific Philosophy. Springer. ISBN 978-3-319-97631-0. Archived from the original on 26 March 2024. Retrieved 29 March 2024.
• Rosenkrantz, Gary S. (2018). "Of Facts and Things". International Journal of Philosophical Studies. 26 (5): 679–700. doi:10.1080/09672559.2018.1542277.
• Runggaldier, Edmund (2009). Unity and Time in Metaphysics. Walter de Gruyter. ISBN 978-3-11-021234-1. Archived from the original on 2024-06-05. Retrieved 2024-06-12.
• Ruzsa, Ferenc. "Sankhya". Internet Encyclopedia of Philosophy. Archived from the original on 19 May 2019. Retrieved 30 March 2024.
• Ryckman, Thomas (2005). The Reign of Relativity: Philosophy in Physics 1915–1925. Oxford University Press. ISBN 978-0-19-029215-7. Archived from the original on 17 March 2024. Retrieved 18 March 2024.
• Sadegh-Zadeh, Kazem (2011). "Fuzzy Formal Ontology". In Seising, Rudolf; González, Veronica Sanz (eds.). Soft Computing in Humanities and Social Sciences. Springer. ISBN 978-3-642-24672-2. Archived from the original on 2024-06-18. Retrieved 2024-06-20.
• Sales, Tiago Prince; Guizzardi, Giancarlo (2017). "'Is It a Fleet or a Collection of Ships?': Ontological Anti-patterns in the Modeling of Part-Whole Relations". In Kirikova, Mārīte; Nørvåg, Kjetil; Papadopoulos, George A. (eds.). Advances in Databases and Information Systems: 21st European Conference, ADBIS 2017, Nicosia, Cyprus, September 24-27, 2017, Proceedings. Springer. ISBN 978-3-319-66917-5. Archived from the original on 2024-06-26. Retrieved 2024-06-26.
• Sankey, Howard (2018). Rationality, Relativism and Incommensurability. Routledge. ISBN 978-0-429-77611-3.
• Sayre-McCord, Geoff (2023a). "Moral Realism". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on April 23, 2020. Retrieved 19 December 2023.
• Schaffer, Jonathan (2009). "On What Grounds What". In Chalmers, David; Manley, David; Wasserman, Ryan (eds.). Metametaphysics: New Essays on the Foundations of Ontology. Oxford University Press. ISBN 978-0-19-954604-6.
• Schaffer, Jonathan (2010). "Monism: The Priority of the Whole". The Philosophical Review. 119 (1): 31–76. doi:10.1215/00318108-2009-025.
• Schaffer, Jonathan (2018). "Monism". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Archived from the original on 6 July 2024. Retrieved 9 June 2024.
• Schalow, Frank (2019). Historical Dictionary of Heidegger's Philosophy. Rowman & Littlefield. ISBN 978-1-5381-2436-9. Archived from the original on 2024-06-19. Retrieved 2024-06-20.
• Scott, Michael W. (2013). "The Anthropology of Ontology (Religious Science?)". The Journal of the Royal Anthropological Institute. 19 (4): 859–872. doi:10.1111/1467-9655.12067. JSTOR 42001687. Archived from the original on 2022-09-24. Retrieved 2022-09-24. Since roughly the 1990s, a growing number of anthropologists have become interested in the study of ontology – the investigation and theorization of diverse experiences and understandings of the nature of being itself. This generally takes the form of ethnographic accounts of indigenous non-Western modes and models of being, presented in more or less explicit contrast with aspects of a Euro-American or modern ontology imputed to conventional anthropology.
• Shaffer, Michael J. (2015). "The Problem of Necessary and Sufficient Conditions and Conceptual Analysis". Metaphilosophy. 46 (4–5): 555–563. doi:10.1111/meta.12158.