Editing Ontology (section)

== Schools of thought ==
=== Realism and anti-realism ===
{{main|Philosophical realism|Anti-realism}}
The term ''realism'' is used for various theories{{efn|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.<ref>{{harvnb|Niiniluoto|2002|pp=1–2, 21, 25–26, 28–29}}</ref>}} that affirm that some kind of phenomenon is real or has mind-independent existence. Ontological realism is the view that there are [[Subjectivity and objectivity (philosophy)|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.<ref>{{multiref | {{harvnb|Niiniluoto|2002|pp=1–2, 21, 25–26}} | {{harvnb|Chalmers|2009|pp=77–78}} | {{harvnb|Sider|2009|pp=385–386}} }}</ref> 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.<ref>{{multiref | {{harvnb|Chalmers|2009|pp=77–78}} | {{harvnb|Sider|2009|pp=385–386}} }}</ref> 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.<ref>{{multiref | {{harvnb|Chalmers|2009|p=78}} | {{harvnb|Hofweber|2023|loc=§ 4.4 Carnap’s rejection of ontology. (L1) meets (O4) and (the end of?) (O2)}} }}</ref>

[[File:Sanzio 01 Plato Aristotle.jpg|thumb|alt=Fresco showing Plato and Aristotle|[[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.<ref>{{harvnb|Niiniluoto|2002|pp=1–2, 21, 25–26, 28–29}}</ref> Realists about universals say that universals have mind-independent existence. According to [[Theory of forms|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. [[Nominalism|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.<ref>{{multiref | {{harvnb|MacLeod|Rubenstein|loc=Lead Section, § 2. Versions of Realism, § 3. Versions of Anti-Realism}} | {{harvnb|Bigelow|1998a|loc=§ 4. Nominalism and Realism}} | {{harvnb|Loux|Crisp|2017|pp=17–19, 45}} | {{harvnb|Niiniluoto|2002|pp=28–29}}}}</ref>

[[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]].<ref>{{multiref | {{harvnb|Blanchette|1998|loc=Lead Section}} | {{harvnb|Moore|1998|loc=Lead Section}} | {{harvnb|Balaguer|2009|p=[https://books.google.com/books?id=mbn35b2ghgkC&pg=PA36 36]}} | {{harvnb|Linnebo|2024|loc=Lead Section}} }}</ref> 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 (philosophy of mathematics)|formalism]], which understands mathematics not as a theory of reality but as a game governed by rules of string manipulation.<ref>{{multiref | {{harvnb|Balaguer|2009|pp=[https://books.google.com/books?id=mbn35b2ghgkC&pg=PA36 36, 44]}} | {{harvnb|Weir|2024|loc=Lead Section}} }}</ref>

[[Modal realism]] is the theory that in addition to the actual world, there are countless [[possible world]]s 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 [[Counterpart theory|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.<ref>{{multiref | {{harvnb|Borghini|2016|pp=[https://books.google.com/books?id=Ifw8CwAAQBAJ&pg=PA91 91–93]}} | {{harvnb|Chihara|2001|pp=[https://doi.org/10.1093/acprof:oso/9780199246557.003.0005 142–143]}} | {{harvnb|Parent|loc=Lead section}} }}</ref>

[[Scientific realism|Scientific realists]] say that the scientific description of the world is an accurate representation of reality.{{efn|The exact definition of the term is disputed.<ref>{{harvnb|Chakravartty|2017|loc=§ 1. What is Scientific Realism?}}</ref>}} It is of particular relevance in regard to things that [[Unobservable|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 [[Instrumentalism|instruments]] to predict observations and the outcomes of experiments.<ref>{{multiref | {{harvnb|Chakravartty|2017|loc=Lead Section, § 1. What is Scientific Realism?}} | {{harvnb|Liston|loc=Lead Section, § 6b. The Observable-Unobservable Distinction}} | {{harvnb|Okasha|2016|pp=[https://books.google.com/books?id=GMqSDAAAQBAJ&pg=PA54 54–55]}} }}</ref>

[[Moral realism|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-realism|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]].<ref>{{multiref | {{harvnb|DeLapp|loc=Lead Section, § 4a. Moral Realisms, § 4b. Moral Relativisms}} | {{harvnb|Sayre-McCord|2023a|loc=Lead Section}} | {{harvnb|Gowans|2021|loc=Lead Section, § 2. Forms and Arguments}} | {{harvnb|Westacott|loc=Lead Section}} | {{harvnb|Dreier|2007|pp=240–241}} }}</ref>

=== 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.<ref>{{multiref | {{harvnb|Van Inwagen|2011|pp=389–390}} | {{harvnb|Paul|2017|pp=32–33}} | {{harvnb|Woznicki|2022|p=97}} }}</ref> For example, some forms of nominalism state that only concrete particulars exist while some forms of [[bundle theory]] state that only properties exist.<ref>{{harvnb|Van Inwagen|2011|pp=389–390}}</ref> 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.<ref>{{multiref | {{harvnb|Van Inwagen|2011|pp=389–390}} | {{harvnb|Paul|2017|pp=32–33}} | {{harvnb|Woznicki|2022|p=97}} }}</ref>

The closely related discussion between [[monism]] and [[Mind–body dualism|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.<ref>{{multiref | {{harvnb|Schaffer|2018|loc=Lead Section}} | {{harvnb|Robinson|2023|loc=§ Lead Section}} }}</ref> [[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.<ref>{{multiref | {{harvnb|McLaughlin|1999|pp=685–691}} | {{harvnb|Kim|2005|p=608}} | {{harvnb|Sprigge|1998|loc=Lead Section}} }}</ref> [[Neutral monism]] occupies a middle ground by saying that both mind and matter are derivative phenomena.<ref>{{multiref | {{harvnb|Stubenberg|Wishon|2023|loc=Lead Section; § 1.3 Mind and Matter Revisited}} | {{harvnb|Griffin|1998}} }}</ref> Dualists state that mind and matter exist as independent principles, either as [[Substance dualism|distinct substances]] or [[Property dualism|different types of properties]].<ref>{{multiref | {{harvnb|Calef|loc=Lead Section}} | {{harvnb|Robinson|2023|loc=§ Lead Section}} }}</ref> In a slightly different sense, monism contrasts with [[Pluralism (philosophy)|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.{{efn|According to some [[Pantheism|pantheists]], this entity is God.<ref>{{harvnb|Levine|2002|pp=[https://books.google.com/books?id=GAYyLrfsZvUC 71–72, 84–85]}}</ref>}} Pluralism is more commonly accepted and says that several distinct entities exist.<ref>{{harvnb|Schaffer|2018|loc=Lead Section}}</ref>

=== By fundamental categories ===
The historically influential [[Substance theory|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.<ref>{{multiref | {{harvnb|Paul|2017|p=34}} | {{harvnb|Robinson|Weir|2024|loc=§ Lead section}} | {{harvnb|O'Conaill|2022|pp=1–3}} }}</ref> 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.<ref>{{multiref | {{harvnb|Paul|2017|pp=34–35}} | {{harvnb|Robinson|Weir|2024|loc=§ 3.2.2. The concept of substratum or 'thin particular'}} }}</ref>

Various alternative ontological theories have been proposed that deny the role of substances as the foundational building blocks of reality.<ref>{{multiref | {{harvnb|O'Conaill|2022|pp=52–53}} | {{harvnb|Robinson|Weir|2024|loc=§ Lead section}} }}</ref> 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.<ref>{{multiref | {{harvnb|O'Conaill|2022|p=53}} | {{harvnb|Esfeld|2020|pp=[https://books.google.com/books?id=OJgIEQAAQBAJ&pg=PA464 464–465]}} }}</ref>{{efn|This view contrasts with atomism, which states that the world is composed of discrete, indivisible units.<ref>{{harvnb|Esfeld|2020|pp=[https://books.google.com/books?id=OJgIEQAAQBAJ&pg=PA459 459–460]}}</ref>}} According to [[Process philosophy|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.<ref>{{multiref | {{harvnb|O'Conaill|2022|p=53}} | {{harvnb|Robinson|Weir|2024|loc=§ Lead section}} | {{harvnb|Rescher|2000|pp=[https://books.google.com/books?id=E6rOyLVeBOcC&pg=PA5 5–6]}} }}</ref> 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_(philosophy)#In_metaphysics|trope]] bundle theory, properties are particular entities that belong to a single bundle.<ref>{{multiref | {{harvnb|Paul|2017|pp=35–37}} | {{harvnb|O'Conaill|2022|pp=52–53}} }}</ref>

Some ontologies focus not on distinct objects but on interrelatedness. According to relationalism, all of reality is relational at its most fundamental level.<ref>{{multiref | {{harvnb|Heil|2009|p=310}} | {{harvnb|Runggaldier|2009|p=[https://books.google.com/books?id=opLRzEaauTUC&pg=PA248 248]}} | {{harvnb|Lupisella|2020|p=[https://books.google.com/books?id=3JTyDwAAQBAJ&pg=PA70 70]}} }}</ref>{{efn|For example, [[Relationalism#Relationalism (theory of space and time)|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.<ref>{{multiref | {{harvnb|Hoefer|Huggett|Read|2023|loc=Lead Section}} | {{harvnb|Benovsky|2016|pp=[https://books.google.com/books?id=4KHWCwAAQBAJ&pg=PA19 19–20]}} | {{harvnb|Romero|2018|p=[https://books.google.com/books?id=5wJ2DwAAQBAJ&pg=PA135 135]}} }}</ref>}} [[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.<ref>{{multiref | {{harvnb|Esfeld|2020|pp=[https://books.google.com/books?id=OJgIEQAAQBAJ&pg=PA461 461–462]}} | {{harvnb|Ladyman|2023|loc=§ 4. Ontic Structural Realism (OSR)}} }}</ref> 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.<ref>{{multiref | {{harvnb|Campbell|2006|p=25 |loc=§ States of affairs}} | {{harvnb|Rosenkrantz|2018|pp=1–4}} | {{harvnb|Armstrong|2010|pp=[https://books.google.com/books?id=pbGI46EoQKEC&pg=PA26 26–28]}} }}</ref>{{efn|This is expressed in a slogan by [[Ludwig Wittgenstein]]: "The world is the totality of facts, not of things".<ref>{{harvnb|Wittgenstein|2001}}</ref>}}

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 (philosophy)|quality]], relation, place, date, posture, state, action, and passion.<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.1 Aristotelian Realism}} | {{harvnb|Studtmann|2024|loc=§ 2. The Ten-Fold Division}} | {{harvnb|Wardy|1998|loc=§ 1. Categories in Aristotle}} }}</ref> An early influential system of categories in Indian philosophy, first proposed in the [[Vaisheshika]] school, distinguishes between six categories: [[dravya|substance]], quality, motion, universal, individuator, and inherence.<ref>{{multiref | {{harvnb|Westerhoff|2019|loc=§ Three important systems of categories: Vaiśeṣika}} | {{harvnb|Kumar|2019|p=[https://books.google.com/books?id=Jr2YDwAAQBAJ&pg=PA34 34]}} }}</ref> [[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.<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.2 Kantian Conceptualism}} | {{harvnb|Wardy|1998|loc=§ 1. Categories in Kant}} }}</ref> In more recent philosophy, theories of categories were developed by [[C. S. Peirce]], [[Edmund Husserl]], [[Samuel Alexander]], [[Roderick Chisholm]], and [[E. J. Lowe (philosopher)|E. J. Lowe]].<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.3 Husserlian Descriptivism, § 1.4 Contemporary Category Systems}} | {{harvnb|Grim|Rescher|2023|p=[https://books.google.com/books?id=KgPPEAAAQBAJ&pg=PT39 39]}} }}</ref>

=== Others ===
The dispute between constituent and relational ontologies{{efn|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.<ref>{{multiref | {{harvnb|Rea|2021|pp=104–105}} | {{harvnb|Heil|2009|p=310}} | {{harvnb|Runggaldier|2009|p=[https://books.google.com/books?id=opLRzEaauTUC&pg=PA248 248]}} | {{harvnb|Lupisella|2020|p=[https://books.google.com/books?id=3JTyDwAAQBAJ&pg=PA70 70]}} }}</ref>}} 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.<ref>{{multiref | {{harvnb|Rea|2021|pp=104–105}} | {{harvnb|Van Inwagen|2011|pp=390–392}} | {{harvnb|Koslicki|2018|p=[https://books.google.com/books?id=th1rDwAAQBAJ&pg=PA11 11]}} | {{harvnb|Rettler|Bailey|2023|loc=§ 3.2 What Objects Are}} }}</ref>

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.<ref>{{multiref | {{harvnb|Houng|2012|pp=[https://books.google.com/books?id=M6T6CAAAQBAJ&pg=PA106 106–110]}} | {{harvnb|Schaffer|2009|pp=347–348, 354–356}} | {{harvnb|Ceder|2018|loc=§ Flat ontology}} }}</ref> 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.<ref>{{multiref | {{harvnb|Schaffer|2010|pp=31, 44–45}} | {{harvnb|Schaffer|2009|pp=354–356}} | {{harvnb|Ceder|2018|loc=§ Flat ontology}} }}</ref> 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.<ref>{{multiref | {{harvnb|Houng|2012|pp=[https://books.google.com/books?id=M6T6CAAAQBAJ&pg=PA106 106–110]}} | {{harvnb|Schaffer|2009|pp=347–348, 354–356}} | {{harvnb|Ceder|2018|loc=§ Flat ontology}} }}</ref>{{efn|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.<ref>{{harvnb|Houng|2012|pp=[https://books.google.com/books?id=M6T6CAAAQBAJ&pg=PA106 106–110]}}</ref>}}

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 part]]s 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.<ref>{{multiref | {{harvnb|Miller|2018|loc=Lead Section}} | {{harvnb|Costa|loc=Lead Section, § 1. Theories of Persistence}} | {{harvnb|Simons|2013|p=[https://books.google.com/books?id=ql27m77IveQC&pg=PA166 166]}} | {{harvnb|Hawley|2023|loc=3. Change and Temporal Parts}} }}</ref>

Differential ontology is a [[poststructuralist]] approach interested in the relation between the concepts of identity and [[Difference (philosophy)|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.<ref>{{multiref | {{harvnb|Cisney|loc=Lead Section}} | {{harvnb|Rae|2020|p=[https://www.cambridge.org/core/books/abs/poststructuralist-agency/deleuze-differential-ontology-and-subjectivity/1C78F8C61B72EBF95B5C687DF75F06E0 33]}} | {{harvnb|Rae|2014|p=86}} }}</ref>

[[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.<ref>{{multiref | {{harvnb|Young|2021|pp=83–84}} | {{harvnb|Isrow|2022|p=[https://books.google.com/books?id=MrB7EAAAQBAJ&pg=PA28 28]}} | {{harvnb|Neyrat|2020|p=[https://books.google.com/books?id=e_nJDwAAQBAJ&pg=PT13 13]}} }}</ref>