Editing Ontology (section)

== Basic concepts<!--'Eleatic principle' redirects here--> ==
=== Being ===
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|footer            = The scope of ontology covers diverse entities, including everyday objects, living beings, celestial bodies, ideas, numbers, and fictional creatures.
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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.{{efn|When used as a countable noun, ''a being'' is the same as ''an entity''.<ref>{{harvnb|Lowe|2005a|p=84}}</ref>}} In its broadest sense, being only contrasts with non-being or nothingness.<ref>{{multiref | {{harvnb|MacIntyre|2006|p=527}} | {{harvnb|Jaroszyński|2023|pp=[https://books.google.com/books?id=LtL7EAAAQBAJ&pg=PA254 254–255]}} | {{harvnb|Lowe|2005a|p=84}} | {{harvnb|Jacquette|2014|pp=[https://books.google.com/books?id=NmPfBQAAQBAJ&pg=PA1 1–2, 12–13]}} }}</ref> It is controversial whether a more substantial analysis of the concept or meaning of being is possible.<ref>{{multiref | {{harvnb|MacIntyre|2006|pp=528–529}} | {{harvnb|Jacquette|2014|pp=[https://books.google.com/books?id=NmPfBQAAQBAJ&pg=PA1 1–2, 12–13]}} }}</ref> One proposal understands being as a property possessed by every entity.<ref>{{multiref | {{harvnb|MacIntyre|2006|pp=528–529}} | {{harvnb|Casati|Fujikawa|loc=§ 2b. Universalism}} }}</ref> Critics argue that a thing without being cannot have properties. This means that properties presuppose being and cannot explain it.<ref>{{multiref | {{harvnb|Nelson|2022|loc=§ 1. Frege and Russell: Existence Is Not a Property of Individuals}} | {{harvnb|Casati|Fujikawa|loc=§ 1. Existence as a Second-Order Property and Its Relation to Quantification}} }}</ref> Another suggestion is that all beings share a set of essential features. According to the '''Eleatic principle''',<!--boldface per WP:R#PLA--> "power is the mark of being", meaning that only entities with [[Causality|causal]] influence truly exist.<ref>{{harvnb|Campbell|2006|p=22}}</ref> 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".<ref>{{multiref | {{harvnb|Van Inwagen|2024|p=280}} | {{harvnb|Deutscher|2021|p=[https://books.google.com/books?id=IQ0mEAAAQBAJ&pg=PA20 20]}} }}</ref>

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.<ref>{{multiref | {{harvnb|MacIntyre|2006|p=527}} | {{harvnb|Zhang|2011|p=[https://books.google.com/books?id=Vl4EEAAAQBAJ&pg=PA220 220]}} | {{harvnb|Hartmann|2012|pp=[https://books.google.com/books?id=4PyJfVZn-rcC&pg=PA46 46–47]}} }}</ref> Another contrast is between being, as what truly exists, and [[Phenomenon|phenomena]], as what appears to exist.<ref>{{harvnb|MacIntyre|2006|p=527}}</ref> In some contexts, being expresses the fact that something is while [[essence]] expresses its [[Quality (philosophy)|qualities]] or what it is like.<ref>{{multiref | {{harvnb|Lowe|2005a|p=84}} | {{harvnb|Ceylan|1993|p=[https://www.jstor.org/stable/20840134 329]}} }}</ref> 

Ontologists often divide being into fundamental classes or highest kinds, called ''[[categories of being]]''.<ref name="Thomasson2022">{{multiref | {{harvnb|Thomasson|2022|loc=Lead Section}} | {{harvnb|Loux|Crisp|2017|pp=11–12}} | {{harvnb|Wardy|1998|loc=Lead Section}} }}</ref> Proposed categories include substance, [[Property (philosophy)|property]], [[Relation (philosophy)|relation]], [[State of affairs (philosophy)|state of affairs]], and [[Event (philosophy)|event]].<ref>{{multiref | {{harvnb|Campbell|2006|pp=23–25}} | {{harvnb|Hoffman|Rosenkrantz|2008|p=[https://books.google.com/books?id=Ngdi0a5o5iYC&pg=PA26 26]}} }}</ref> 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.<ref name="Thomasson2022"/> 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 [[Univocity of being|everything exists in the same way]].<ref>{{multiref | {{harvnb|Widder|2009|pp=[https://books.google.com/books?id=tvWqBgAAQBAJ&pg=PA32 32–35]}} | {{harvnb|LaZella|2019|p=[https://books.google.com/books?id=NCqODwAAQBAJ&pg=PA17 17]}} }}</ref> 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.<ref>{{multiref | {{harvnb|Daly|2009|pp=[https://books.google.com/books?id=Bt99AgAAQBAJ&pg=PA227 227–228]}} | {{harvnb|Van Inwagen|2023}} | {{harvnb|Casati|Fujikawa|loc=§3. How Many Ways of Being Existent?}} | {{harvnb|Gibson|1998|pp=5–8}} }}</ref>

The relation between being and non-being is a frequent topic in ontology. Influential issues include the status of [[nonexistent objects]]<ref>{{multiref | {{harvnb|Reicher|2022|loc=[https://plato.stanford.edu/entries/nonexistent-objects/ lead section, §1. The Concept of a Nonexistent Object]}} | {{harvnb|Gibson|1998|p=8}} | {{harvnb|Yao|2014|p=[https://books.google.com/books?id=NZjOAwAAQBAJ&pg=PA140 140]}} }}</ref> and [[Why is there anything at all?|why there is something rather than nothing]].<ref>{{multiref | {{harvnb|Lowe|2005b|p=277}} | {{harvnb|Casati|Fujikawa|loc=Lead Section, §4. Why Is There Something Rather Than Nothing?}} | {{harvnb|Sorensen|2023|loc=Lead Section, §1. Why Is There Something Rather Than Nothing?}} | {{harvnb|Pruss|Rasmussen|2018|pp=4–5}}}}</ref>

=== Particulars and universals ===
{{main|Particular|Universal (metaphysics)|l1=Particulars|l2=Universals}}

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|footer            = The [[Taj Mahal]] is a particular entity while the color ''green'' is a universal entity.
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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]].<ref>{{multiref | {{harvnb|Lowe|2005|p=683}} | {{harvnb|MacLeod|Rubenstein|loc=Lead Section, § 1a. The Nature of Universals}} | {{harvnb|Bigelow|1998|loc=Lead Section}} | {{harvnb|Campbell|2006|loc=§ Particularity and Individuality}} | {{harvnb|Maurin|2019|loc=Lead Section}} }}</ref> 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''.<ref>{{multiref | {{harvnb|MacLeod|Rubenstein|loc=Lead Section}} | {{harvnb|Bigelow|1998a|loc=Lead Section}} | {{harvnb|Cowling|2019|loc=Lead Section}} | {{harvnb|Loux|Crisp|2017|pp=17–19}} }}</ref>

Universals can take the form of properties or relations.<ref>{{multiref | {{harvnb|Campbell|2006|pp=24–25}} | {{harvnb|Bigelow|1998|loc=Lead Section}} }}</ref>{{efn|This idea is opposed by trope theorists, who understand properties and relations as particular entities.<ref>{{harvnb|Campbell|2006|p=25}}</ref>}} Properties describe the characteristics of things. They are features or qualities possessed by an entity.<ref>{{multiref | {{harvnb|Campbell|2006|p=24}} | {{harvnb|Orilia|Paolini Paoletti|2022|loc=Lead Section}} }}</ref> Properties are often divided into [[Property (philosophy)#Essential and accidental|essential and accidental properties]]. A property is essential if an entity must have it; it is accidental if the entity can exist without it.<ref>{{harvnb|Orilia|Paolini Paoletti|2022|loc=§ 1.7 Kinds of Properties}}</ref> For instance, ''having three sides'' is an essential property of a triangle, whereas ''being red'' is an accidental property.<ref>{{harvnb|Vaidya|Wallner|2024|p=[https://books.google.com/books?id=W34IEQAAQBAJ&pg=PA473 473]}}</ref>{{efn|Other influential distinctions are between intrinsic and extrinsic properties, between determinate or determinable properties, and between categorical and dispositional properties.<ref>{{multiref | {{harvnb|Orilia|Paolini Paoletti|2022|loc=§ 1.7 Kinds of Properties, § 5.2. Essentially Categorical vs. Essentially Dispositional Properties}} | {{harvnb|Marshall|Weatherson|2023|loc=Lead Section}} }}</ref>}} 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.<ref>{{multiref | {{harvnb|Sider|2010|p=[https://books.google.com/books?id=-KkPEAAAQBAJ&pg=PA13 13]}} | {{harvnb|Bogen|2005|p=798}} | {{harvnb|MacBride|2020|loc=lead section}} | {{harvnb|Campbell|2006|p=25}} }}</ref> 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]]".<ref>{{harvnb|MacBride|2020|loc=§ 2. Eliminativism, External Relations and Bradley’s Regress}}</ref> Relations are often divided into [[Relation (philosophy)#Internal and external|internal and external relations]]. Internal relations depend only on the properties of the objects they connect, like the relation of [[Similarity (philosophy)|resemblance]]. External relations express characteristics that go beyond what the connected objects are like, such as spatial relations.<ref>{{multiref | {{harvnb|MacBride|2020|loc=§1. Preliminary Distinctions}} | {{harvnb|Heil|2009|p=316}} | {{harvnb|Armstrong|2010|pp=24–25}} }}</ref>

Substances{{efn|The term ''substance'' has a specific meaning in philosophy distinct from ordinary language expressions such as ''chemical substance'' or ''substance abuse''.<ref>{{harvnb|O'Conaill|2022|p=1}}</ref>}} 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''.<ref>{{multiref | {{harvnb|Campbell|2006|pp=23–24}} | {{harvnb|O'Conaill|2022|pp=1–2, 12–13, 29}} | {{harvnb|Robinson|Weir|2024|loc=Lead Section}} }}</ref>

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 ''[[fact]]s''.<ref>{{multiref | {{harvnb|Campbell|2006|p=25}} | {{harvnb|Textor|2021|loc=Lead Section}} }}</ref>{{efn|David Armstrong and his followers use a different terminology that does not distinguish between states of affairs and facts.<ref>{{harvnb|Textor|2021|loc=Lead Section}}</ref>}} Facts are [[Truthmaker theory|truthmakers]] of statements, meaning that whether a statement is true or false depends on the underlying facts.<ref>{{harvnb|Textor|2021|loc=Lead Section}}</ref>

Events are particular entities{{efn|Some ontologists also use the term in a less common sense to refer to universals in the form of event types.<ref>{{harvnb|Mackie|2005|p=272}}</ref>}} 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.<ref>{{multiref | {{harvnb|Mackie|2005|p=272}} | {{harvnb|Campbell|2006|p=25}} }}</ref> Complex events, also called ''processes'', are composed of a sequence of events.<ref>{{harvnb|Campbell|2006|p=25}}</ref>

=== Concrete and abstract objects ===
{{Main|Abstract and concrete|l1=Concrete and abstract}}
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 [[integer]]s. They lack causal powers and do not undergo changes.<ref>{{multiref | {{harvnb|Mackie|1998|loc=Lead Section}} | {{harvnb|Falguera|Martínez-Vidal|Rosen|2022|loc=[https://plato.stanford.edu/entries/abstract-objects/ lead section, § 1. Introduction]}} | {{harvnb|Faye|2013|pp=[https://books.google.com/books?id=ftrmBQAAQBAJ&pg=PA89 89–91]}} | {{harvnb|Prior|2006|pp=498–499}} | {{harvnb|Oliver|2005|p=3}} }}</ref>{{efn|The precise definition is disputed.<ref>{{harvnb|Oliver|2005|p=3}}</ref>}} The existence and nature of abstract objects remain subjects of philosophical debate.<ref>{{multiref | {{harvnb|Oliver|2005|p=3}} | {{harvnb|Plebani|2013|p=[https://books.google.com/books?id=pkNb_3NYyz0C&pg=PA5 5]}} }}</ref>

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 [[molecule]]s, [[atom]]s, and [[elementary particle]]s.<ref>{{multiref | {{harvnb|Cornell|loc=Lead Section}} | {{harvnb|Loux|Crisp|2017|pp=250–251}} | {{harvnb|Varzi|2019|loc=Lead Section, § 1. 'Part' and Parthood}} | {{harvnb|Cornell|loc=Lead Section, § 2. The Special Composition Question}} | {{harvnb|Tallant|2017|pp=19–21}} }}</ref> [[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.<ref>{{multiref |  {{harvnb|Loux|Crisp|2017|pp=82–83}} | {{harvnb|Cornell|loc=Lead Section, § 2. The Special Composition Question}} | {{harvnb|Brenner|2015|p=1295}} | {{harvnb|Tallant|2017|pp=19–21, 23–24, 32–33}} | {{harvnb|Cornell|loc=Lead Section}}}}</ref> 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.<ref>{{multiref | {{harvnb|Rea|1997|pp=[https://books.google.com/books?id=a0QOWVtDOXYC&pg=PR15 xv–xvi]}} | {{harvnb|Korman|2021|loc=Lead Section}} }}</ref>

Abstract objects are closely related to fictional and [[Object of the mind|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]].<ref>{{multiref | {{harvnb|Kroon|Voltolini|2023|loc=Lead Section}} | {{harvnb|Lamarque|1998|loc=Lead Section}} | {{harvnb|Prior|2006|p=493}} }}</ref> 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.<ref>{{multiref | {{harvnb|Kroon|Voltolini|2023|loc=§ 1. The Metaphysics of Fictional Entities}} | {{harvnb|Lamarque|1998|loc=§ 3. Hospitable theories}} }}</ref> Intentional objects are entities that exist within [[mental states]], like [[perception]]s, [[belief]]s, and [[desire]]s. 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 [[Intentionality#The problem of intentional inexistence|ontological status of intentional objects]].<ref>{{multiref | {{harvnb|Jacob|2023|loc=2. Intentional inexistence}} | {{harvnb|Kriegel|2007|pp=307–308}} | {{harvnb|O’Madagain|loc=§ 2. Intentional Objects}} }}</ref>

=== 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.<ref>{{multiref | {{harvnb|Ney|2014|pp=53–55}} | {{harvnb|Fine|1995|pp=269–270}} }}</ref> For instance, the surface of an apple cannot exist without the apple.<ref>{{harvnb|Nuñez Erices|2019|pp=15–16}}</ref> 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.<ref>{{multiref | {{harvnb|Ney|2014|pp=53–55}} | {{harvnb|Fine|1995|pp=269–270}} }}</ref> It is closely related to [[Grounding (metaphysics)|metaphysical grounding]], which is the relation between a ground and the facts it explains.<ref>{{multiref | {{harvnb|Tahko|Lowe|2020|loc=§ 5. Ontological Dependence and Metaphysical Grounding}} | {{harvnb|Ney|2014|pp=53–55}} }}</ref>

[[File:Willard Van Orman Quine on Bluenose II in Halifax NS harbor 1980.jpg|thumb|upright=.8|alt=Photo of Willard Van Orman Quine|[[Willard Van Orman Quine]] used the concept of [[ontological commitment]]s to analyze theories.]]

An [[ontological commitment]] of a person or a theory is an entity that exists according to them.<ref>{{multiref | {{harvnb|Ney|2014|p=31}} | {{harvnb|Jubien|1998|loc=Lead Section}} }}</ref> For instance, a person who [[Theism|believes in God]] has an ontological commitment to [[God]].<ref>{{harvnb|Jubien|1998|loc=Lead Section}}</ref> 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.<ref>{{multiref | {{harvnb|Colyvan|2001|p=23}} | {{harvnb|Bangu|2012|pp=26–27}} | {{harvnb|Ney|2014|pp=40–43}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 4. The Methodology of Metaphysics}} }}</ref>

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 world]]s to analyze possibility and necessity.<ref>{{multiref | {{harvnb|Parent|loc=Lead Section}} | {{harvnb|Loux|Crisp|2017|pp=149–150}} | {{harvnb|Koons|Pickavance|2015|pp=154–155}} | {{harvnb|Mumford|2012|loc=§ 8. What Is Possible?}} }}</ref> A possible world is a complete and consistent way how things could have been.<ref>{{multiref | {{harvnb|Berto|Jago|2023|loc=Lead Section}} | {{harvnb|Pavel|1986|p=[https://books.google.com/books?id=OF7ZA54UpYYC&pg=PA50 50]}} }}</ref> 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.<ref>{{multiref | {{harvnb|Menzel|2023|loc=Lead Section, § 1. Possible Worlds and Modal Logic}} | {{harvnb|Kuhn|2010|p=[https://books.google.com/books?id=c_eYe6NVaDMC&pg=PA13 13]}} }}</ref> The field of [[modal logic]] provides a precise formalization of the concepts of possibility and necessity.<ref>{{harvnb|Garson|2024|loc=Lead section, § 1. What is Modal Logic?}}</ref>

In ontology, [[Identity (philosophy)|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.<ref>{{multiref | {{harvnb|Kirwan|2005|pp=417–418}} | {{harvnb|Noonan|Curtis|2022|loc=Lead Section}} | {{harvnb|Kuhlmann|2010|pp=1867–1867b}} }}</ref> 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".<ref>{{multiref | {{harvnb|Gallois|2016|loc=§ 2.1 Diachronic and Synchronic Identity}} | {{harvnb|Noonan|Curtis|2022|loc=Lead Section, § 5. Identity Over Time}} }}</ref> The notion of identity also has a number of philosophical implications in terms of how it interacts with the aforementioned necessity and possibility. Most famously, Saul Kripke contended that ''discovered identities'' such as "Water is H<small>2</small>O" are necessarily true because "H<small>2</small>O" is what's known as a [[rigid designator]]. <ref>{{cite book |last1=Kripke |first1=Saul |title=Naming and Necessity |date=1980 |publisher=Harvard University Press, Blackwell |isbn=978-0-674-59845-4 |pages=128-129}}</ref>