Ontology Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.Anti-spam check. Do not fill this in! == Overview<!--'Eleatic principle' redirects here--> == Ontology is closely associated with Aristotle's question of 'being ''qua'' being': the question of what all entities in the widest sense have in common.<ref name="Borchert2"/><ref>{{cite book |last=Sandkühler |first=Hans Jörg |url=https://meiner.de/enzyklopadie-philosophie.html |title=Enzyklopädie Philosophie |date=2010 |publisher=Meiner |language=de |chapter=Ontologie: 2.1 Antike |quote=Nach einer berühmten Formulierung von Aristoteles (384–322 v. Chr.), der zwar wie auch Platon nicht den Ausdruck ›O.‹ verwendet, sich jedoch der Sache nach in seiner ›ersten Philosophie‹ ausführlich damit befasst, lässt sich O. charakterisieren als die Untersuchung des Seienden als Seiendem (to on he on). |access-date=2020-12-16 |archive-url=https://web.archive.org/web/20210311040207/https://meiner.de/enzyklopadie-philosophie.html |archive-date=2021-03-11 |url-status=dead}}</ref> The '''Eleatic principle'''<!--boldface per WP:R#PLA--> is one answer to this question: it states that being is inextricably tied to causation, that "Power is the mark of Being".<ref name="Borchert2">{{cite book |last=Borchert |first=Donald |title=Macmillan Encyclopedia of Philosophy, 2nd Edition |date=2006 |publisher=Macmillan |url=https://philpapers.org/rec/MONMEO-3 |chapter=Ontology}}</ref> One problem with this answer is that it excludes abstract objects. Another explicit but little-accepted answer can be found in Berkeley's slogan that "to be is to be perceived".<ref>{{cite web |last=Flage |first=Daniel E. |title=Berkeley, George |url=https://iep.utm.edu/berkeley/ |website=Internet Encyclopedia of Philosophy |access-date=4 January 2021}}</ref> Intimately related but not identical to the question of 'being ''qua'' being' is the problem of [[Category of being|categories]].<ref name="Borchert2"/> Categories are usually seen as the highest kinds or genera.<ref name="Thomasson2"/> A system of categories provides a classification of entities that is exclusive and exhaustive: every entity belongs to exactly one category. Various such classifications have been proposed, often including categories for [[Substance theory|substances]], [[Property (philosophy)|properties]], [[Relations (philosophy)|relations]], [[State of affairs (philosophy)|states of affairs]], and [[Event (philosophy)|events]].<ref name="Borchert2"/><ref name="Sandkühler2">{{cite book |last=Sandkühler |first=Hans Jörg |url=https://meiner.de/enzyklopadie-philosophie.html |title=Enzyklopädie Philosophie |date=2010 |publisher=Meiner |language=de |chapter=Ontologie: 4 Aktuelle Debatten und Gesamtentwürfe |access-date=2020-12-16 |archive-url=https://web.archive.org/web/20210311040207/https://meiner.de/enzyklopadie-philosophie.html |archive-date=2021-03-11 |url-status=dead}}</ref> At the core of the differentiation between categories are various fundamental ontological concepts and distinctions, for example, the concepts of ''particularity and universality'', of ''abstractness and concreteness'', of ''ontological dependence'', of ''identity'', and of ''modality''.<ref name="Borchert2"/><ref name="Sandkühler2"/> These concepts are sometimes treated as categories themselves, and are used to explain the difference between categories or play other central roles for characterizing different ontological theories. Within ontology, there is a lack of general consensus concerning how the different categories are to be defined.<ref name="Thomasson2"/> Different ontologists often disagree on whether a certain category has any members at all or whether a given category is fundamental.<ref name="Sandkühler2"/> === Particulars and universals === [[Particular]]s or individuals are usually contrasted with [[Universal (metaphysics)|universals]].<ref>{{cite book |last=Honderich |first=Ted |title=The Oxford Companion to Philosophy |date=2005 |publisher=Oxford University Press |url=https://philpapers.org/rec/HONTOC-2 |chapter=particulars and non-particulars}}</ref><ref>{{cite book |last=Craig |first=Edward |title=Routledge Encyclopedia of Philosophy |date=1996 |publisher=Routledge |url=https://philpapers.org/rec/BEAREO |chapter=Particulars}}</ref> Universals concern features that can be exemplified by various different particulars.<ref name="MacLeod">{{cite web |last=MacLeod |first=Mary C. |title=Universals |url=https://iep.utm.edu/universa/ |website=Internet Encyclopedia of Philosophy |access-date=4 January 2021}}</ref> For example, a tomato and a strawberry are two particulars that exemplify the universal redness. Universals can be present at various distinct locations in space at the same time while particulars are restricted to one location at a time. Furthermore, universals can be fully present at different times, which is why they are sometimes referred to as ''repeatables'' in contrast to non-repeatable particulars.<ref name="Sandkühler2"/> The so-called [[problem of universals]] is the problem to explain how different things can agree in their features, e.g., how a tomato and a strawberry can both be red.<ref name="Borchert2"/><ref name="MacLeod"/> [[Problem of universals#realism|Realists]] believe that there are universals. They can solve the ''problem of universals'' by explaining the commonality through a universal shared by both entities.<ref name="Sandkühler2"/> Realists are divided among themselves as to whether universals can exist independently of being exemplified by something ("''ante res''") or not ("''in rebus''").<ref>{{cite web |title=Realism – Universals |url=https://www.britannica.com/topic/realism-philosophy/Universals |website=Encyclopedia Britannica |access-date=4 January 2021 |language=en}}</ref> [[Nominalism|Nominalists]], on the other hand, deny that there are universals. They use other notions to explain how a feature can be common to several entities, for example, by positing either fundamental resemblance-relations between the entities (resemblance nominalism) or a shared membership to a common natural class (class nominalism).<ref name="Sandkühler2"/> === Abstract and concrete === {{main|Abstract and concrete}} Many philosophers agree that there is an exclusive and exhaustive distinction between ''concrete objects'' and ''abstract objects''.<ref name="Sandkühler2"/> Some philosophers consider this to be the most general division of being.<ref name="Honderich">{{cite book |last=Honderich |first=Ted |title=The Oxford Companion to Philosophy |date=2005 |publisher=Oxford University Press |url=https://philpapers.org/rec/HONTOC-2 |chapter=Ontology}}</ref> Examples of concrete objects include plants, human beings, and planets while things like numbers, sets, and propositions are abstract objects.<ref>{{cite web |last=Rosen |first=Gideon |title=Abstract Objects |url=https://plato.stanford.edu/entries/abstract-objects/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=4 January 2021 |date=2020}}</ref> But despite the general agreement concerning the paradigm cases, there is less consensus as to what the characteristic marks of concreteness and abstractness are. Popular suggestions include defining the distinction in terms of the difference between (1) existence inside or outside [[spacetime]], (2) having causes and effects or not, and (3) having contingent or necessary existence.<ref>{{cite book |last=Honderich |first=Ted |title=The Oxford Companion to Philosophy |date=2005 |publisher=Oxford University Press |url=https://philpapers.org/rec/HONTOC-2 |chapter=abstract entities}}</ref><ref>{{cite book |last=Craig |first=Edward |title=Routledge Encyclopedia of Philosophy |date=1996 |publisher=Routledge |url=https://philpapers.org/rec/BEAREO |chapter=Abstract objects}}</ref> === Ontological dependence === {{main|Grounding (metaphysics)}} An entity ''ontologically depends'' on another entity if the first entity cannot exist without the second entity. Ontologically independent entities, on the other hand, can exist all by themselves.<ref>{{cite book |last=Sandkühler |first=Hans Jörg |url=https://meiner.de/enzyklopadie-philosophie.html |title=Enzyklopädie Philosophie |date=2010 |publisher=Meiner |language=de |section=Ontologie: 4.2.3 Ontologische Unabhängigkeit. Ganz grob gesagt versteht man unter existenzieller oder ontologischer (im Gegensatz z.B. zu logischer) Unabhängigkeit die Fähigkeit, ›alleine zu existieren‹. |access-date=2020-12-16 |archive-url=https://web.archive.org/web/20210311040207/https://meiner.de/enzyklopadie-philosophie.html |archive-date=2021-03-11 |url-status=dead}}</ref> For example, the surface of an apple cannot exist without the apple and so depends on it ontologically.<ref>{{cite web |last=Varzi |first=Achille |title=Boundary |url=https://plato.stanford.edu/entries/boundary/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=4 January 2021 |date=2015}}</ref> Entities often characterized as ontologically dependent include properties, which depend on their bearers, and boundaries, which depend on the entity they demarcate from its surroundings.<ref name="Tahko">{{cite web |last1=Tahko |first1=Tuomas E. |last2=Lowe |first2=E. Jonathan |title=Ontological Dependence |url=https://plato.stanford.edu/entries/dependence-ontological/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=4 January 2021 |date=2020}}</ref> As these examples suggest, ontological dependence is to be distinguished from causal dependence, in which an effect depends for its existence on a cause. It is often important to draw a distinction between two types of ontological dependence: rigid and generic.<ref name="Sandkühler2"/><ref name="Tahko"/> Rigid dependence concerns the dependence on one specific entity, as the surface of an apple depends on its specific apple.<ref name="Erices">{{cite journal |last=Erices |first=Gonzalo Nuñez |title=Boundaries and Things. A Metaphysical Study of the Brentano-Chisholm Theory |journal=Kriterion: Journal of Philosophy |date=2019 |volume=33 |issue=2 |pages=15–48 |doi=10.1515/krt-2019-330203 |s2cid=245494576 |url=https://philpapers.org/rec/ERIBAT|doi-access=free }}</ref> Generic dependence, by contrast, involves a weaker form of dependence, on merely a certain type of entity. For example, electricity generically depends on there being charged particles, but it does not depend on any specific charged particle.<ref name="Tahko"/> Dependence-relations are relevant to ontology since it is often held that ontologically dependent entities have a less robust form of being. This way a ''hierarchy'' is introduced into the world that brings with it the distinction between more and less fundamental entities.<ref name="Tahko"/> === Identity === [[Identity (philosophy)|Identity]] is a basic ontological concept that is often expressed by the word "same".<ref name="Sandkühler2"/><ref name="Noonan">{{cite web |last1=Noonan |first1=Harold |last2=Curtis |first2=Ben |title=Identity |url=https://plato.stanford.edu/entries/identity/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=4 January 2021 |date=2018}}</ref> It is important to distinguish between ''qualitative identity'' and ''numerical identity''. For example, consider two children with identical bicycles engaged in a race while their mother is watching. The two children have the ''same'' bicycle in one sense (''qualitative identity'') and the ''same'' mother in another sense (''numerical identity'').<ref name="Sandkühler2"/> Two qualitatively identical things are often said to be indiscernible. The two senses of ''sameness'' are linked by two principles: the principle of ''indiscernibility of identicals'' and the principle of ''[[identity of indiscernibles]]''. The principle of ''indiscernibility of identicals'' is uncontroversial and states that if two entities are numerically identical with each other then they exactly resemble each other.<ref name="Noonan"/> The principle of ''identity of indiscernibles'', on the other hand, is more controversial in making the converse claim that if two entities exactly resemble each other then they must be numerically identical.<ref name="Noonan"/> This entails that "no two distinct things exactly resemble each other".<ref>{{cite web |last=Forrest |first=Peter |title=The Identity of Indiscernibles |url=https://plato.stanford.edu/entries/identity-indiscernible/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=20 January 2021 |date=2020}}</ref> A well-known counterexample comes from [[Max Black]], who describes a symmetrical universe consisting of only two spheres with the same features.<ref>{{cite journal |last=Black |first=Max |title=The Identity of Indiscernibles |journal=Mind |date=1952 |volume=61 |issue=242 |pages=153–164 |doi=10.1093/mind/LXI.242.153 |url=https://philpapers.org/rec/BLATIO-5}}</ref> Black argues that the two spheres are indiscernible but not identical, thereby constituting a violation of the principle of ''identity of indiscernibles''.<ref>{{cite journal |last=Cowling |first=Sam |title=Non-Qualitative Properties |journal=Erkenntnis |date=2015 |volume=80 |issue=2 |pages=275–301 |doi=10.1007/s10670-014-9626-9 |s2cid=122265064 |url=https://philpapers.org/rec/COWNP}}</ref> The problem of ''identity over time'' concerns the question of ''persistence'': whether or in what sense two objects at different times can be ''numerically identical''. This is usually referred to as ''diachronic identity'' in contrast to ''synchronic identity''.<ref name="Noonan"/><ref name="Gallois">{{cite web |last=Gallois |first=Andre |title=Identity Over Time |url=https://plato.stanford.edu/entries/identity-time/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=23 January 2021 |date=2016}}</ref> The statement that "[t]he table in the next room is identical with the one you purchased last year" asserts diachronic identity between the table now and the table then.<ref name="Gallois"/> A famous example of a denial of diachronic identity comes from [[Heraclitus]], who argues that it is impossible to step into the same river twice because of the changes that occurred in-between.<ref name="Noonan"/><ref name="Costa"/> The traditional position on the problem of ''persistence'' is [[endurantism]], the thesis that diachronic identity in a strict sense is possible. One problem with this position is that it seems to violate the principle of ''indiscernibility of identicals'': the object may have undergone changes in the meantime resulting in it being discernible from itself.<ref name="Sandkühler2"/> [[Perdurantism]] or [[four-dimensionalism]] is an alternative approach holding that ''diachronic identity'' is possible only in a loose sense: while the two objects differ from each other strictly speaking, they are both temporal parts that belong to the same temporally extended whole.<ref name="Sandkühler2"/><ref>{{cite web |last=Hawley |first=Katherine |title=Temporal Parts |url=https://plato.stanford.edu/entries/temporal-parts/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=23 January 2021 |date=2020}}</ref> ''Perdurantism'' avoids many philosophical problems plaguing ''endurantism'', but ''endurantism'' seems to be more in touch with how we ordinarily conceive ''diachronic identity''.<ref name="Gallois"/><ref name="Costa">{{cite web |last=Costa |first=Damiano |title=Persistence in Time |url=https://iep.utm.edu/per-time/ |website=Internet Encyclopedia of Philosophy |access-date=23 January 2021}}</ref> === Modality === [[Modal logic|Modality]] concerns the concepts of possibility, actuality, and necessity. In contemporary discourse, these concepts are often defined in terms of [[possible worlds]].<ref name="Sandkühler2"/> A possible world is a complete way how things could have been.<ref>{{cite journal |last=Vander Laan |first=David A. |date=1997 |title=The Ontology of Impossible Worlds |url=https://philpapers.org/rec/VANTOO |journal=Notre Dame Journal of Formal Logic |volume=38 |issue=4 |pages=597–620 |doi=10.1305/ndjfl/1039540772 |doi-access=free}}</ref> The actual world is one possible world among others: things could have been different from what they actually are. A proposition is possibly true if there is at least one possible world in which it is true; it is necessarily true if it is true in all possible worlds.<ref>{{cite web |last=Menzel |first=Christopher |title=Possible Worlds |url=https://plato.stanford.edu/entries/possible-worlds/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=5 January 2021 |date=2017}}</ref> ''[[Actualism|Actualists]]'' and ''possibilists'' disagree on the ''ontological status'' of possible worlds.<ref name="Sandkühler2"/> Actualists hold that reality is at its core actual and that possible worlds should be understood in terms of actual entities, for example, as fictions or as sets of sentences.<ref name="Parent">{{cite web |last=Parent |first=Ted |title=Modal Metaphysics |url=https://iep.utm.edu/mod-meta/ |website=Internet Encyclopedia of Philosophy |access-date=5 January 2021}}</ref> Possibilists, on the other hand, assign to possible worlds the same ''fundamental ontological status'' as to the actual world. This is a form of [[modal realism]], holding that reality has ''irreducibly modal features''.<ref name="Parent"/> Another important issue in this field concerns the distinction between ''contingent'' and ''necessary beings''.<ref name="Sandkühler2"/> Contingent beings are beings whose existence is possible but not necessary. Necessary beings, on the other hand, could not have failed to exist.<ref>{{cite web |last=Davidson |first=Matthew |title=God and Other Necessary Beings |url=https://plato.stanford.edu/entries/god-necessary-being/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=5 January 2021 |date=2019}}</ref><ref>{{cite web |last=Reichenbach |first=Bruce |title=Cosmological Argument |url=https://plato.stanford.edu/entries/cosmological-argument/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=6 January 2021 |date=2019}}</ref> It has been suggested that this distinction is the highest division of being.<ref name="Sandkühler2"/><ref>{{cite web |title=Contingent |url=https://www.newadvent.org/cathen/04331a.htm |website=newadvent.org |publisher=CATHOLIC ENCYCLOPEDIA |access-date=5 January 2021}}</ref> === Substances === The category of ''substances'' has played a central role in many ontological theories throughout the history of philosophy.<ref name="kim">{{cite book |last1=Kim |first1=Jaegwon |last2=Sosa |first2=Ernest |last3=Rosenkrantz |first3=Gary S. |title=A Companion to Metaphysics |publisher=Wiley-Blackwell |url=https://philpapers.org/rec/KIMACT-9 |chapter=substance|year=1994 }}</ref><ref name="Robinson"/> "Substance" is a technical term within philosophy not to be confused with the more common usage in the sense of chemical substances like gold or sulfur. Various definitions have been given but among the most common features ascribed to substances in the philosophical sense is that they are ''particulars'' that are ''ontologically independent'': they are able to exist all by themselves.<ref name="Borchert2"/><ref name="kim"/> Being ontologically independent, substances can play the role of ''fundamental entities'' in the ''ontological hierarchy''.<ref name="Tahko"/><ref name="Robinson">{{cite web |last=Robinson |first=Howard |title=Substance |url=https://plato.stanford.edu/entries/substance/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |date=2020}}</ref> If 'ontological independence' is defined as including ''causal independence'', then only self-caused entities, like Spinoza's God, can be substances. With a specifically ontological definition of 'independence', many everyday objects like books or cats may qualify as substances.<ref name="Borchert2"/><ref name="kim"/> Another defining feature often attributed to substances is their ability to ''undergo changes''. Changes involve something existing ''before'', ''during'', and ''after'' the change. They can be described in terms of a persisting substance gaining or losing properties, or of ''matter'' changing its ''form''.<ref name="kim" /> From this perspective, the ripening of a tomato may be described as a change in which the tomato loses its greenness and gains its redness. It is sometimes held that a substance can have a property in two ways: ''[[Essence|essentially]]'' and ''accidentally''. A substance can survive a change of ''accidental properties'', but it cannot lose its ''essential properties'', which constitute its nature.<ref name="Robinson"/><ref name="Robertson">{{cite web |last1=Robertson Ishii |first1=Teresa |last2=Atkins |first2=Philip |title=Essential vs. Accidental Properties |url=https://plato.stanford.edu/entries/essential-accidental/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |date=2020}}</ref> === Properties and relations === {{main|Property (philosophy)|Relations (philosophy)}} The category of ''properties'' consists of entities that can be exemplified by other entities, e.g., by substances.<ref name="Orilia">{{cite web |last1=Orilia |first1=Francesco |last2=Paolini Paoletti |first2=Michele |title=Properties |url=https://plato.stanford.edu/entries/properties/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |date=2020}}</ref> Properties characterize their bearers, they express what their bearer is like.<ref name="Borchert2"/> For example, the red color and the round shape of an apple are properties of this apple. Various ways have been suggested concerning how to conceive properties themselves and their relation to substances.<ref name="Sandkühler2"/> The traditionally dominant view is that properties are universals that inhere in their bearers.<ref name="Borchert2"/> As universals, they can be shared by different substances. Nominalists, on the other hand, deny that universals exist.<ref name="MacLeod"/> Some nominalists try to account for properties in terms of resemblance relations or class membership.<ref name="Sandkühler2"/> Another alternative for nominalists is to conceptualize properties as simple particulars, so-called [[Trope (philosophy)#In metaphysics|tropes]].<ref name="Borchert2"/> This position entails that both the apple and its redness are particulars. Different apples may still exactly resemble each other concerning their color, but they do not share the same particular property on this view: the two color-tropes are ''numerically distinct''.<ref name="MacLeod"/> Another important question for any theory of properties is how to conceive the relation between a bearer and its properties.<ref name="Sandkühler2"/> Substratum theorists hold that there is some kind of substance, ''substratum'', or ''[[Substance theory#Bare particular|bare particular]]'' that acts as bearer.<ref name="Benovsky">{{cite journal |last=Benovsky |first=Jiri |title=The Bundle Theory and the Substratum Theory: Deadly Enemies or Twin Brothers? |journal=Philosophical Studies |date=2008 |volume=141 |issue=2 |pages=175–190 |doi=10.1007/s11098-007-9158-0 |s2cid=18712931 |url=https://philpapers.org/rec/BENTBT-2}}</ref> [[Bundle theory]] is an alternative view that does away with a substratum altogether: objects are taken to be just a bundle of properties.<ref name="Robinson"/><ref>{{cite journal |last=Rodriguez-Pereyra |first=Gonzalo |title=The Bundle Theory is Compatible with Distinct but Indiscernible Particulars |journal=Analysis |date=2004 |volume=64 |issue=1 |pages=72–81 |doi=10.1093/analys/64.1.72 |url=https://philpapers.org/rec/ERETBT}}</ref> They are held together not by a substratum but by the so-called ''compresence-relation'' responsible for the bundling. Both substratum theory and bundle theory can be combined with conceptualizing properties as universals or as particulars.<ref name="Benovsky"/> An important distinction among properties is between ''categorical'' and ''dispositional'' properties.<ref name="Borchert2"/><ref name="Kriegel"/> Categorical properties concern what something is like, e.g., what qualities it has. Dispositional properties, on the other hand, involve what powers something has, what it is able to do, even if it is not actually doing it.<ref name="Borchert2"/> For example, the shape of a sugar cube is a categorical property, while its tendency to dissolve in water is a dispositional property. For many properties there is a lack of consensus as to how they should be classified, for example, whether colors are categorical or dispositional properties.<ref name="Choi">{{cite web |last1=Choi |first1=Sungho |last2=Fara |first2=Michael |title=Dispositions |url=https://plato.stanford.edu/entries/dispositions/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |date=2018}}</ref><ref>{{cite web |last=Rubenstein |first=Eric M. |title=Color |url=https://iep.utm.edu/color/ |website=Internet Encyclopedia of Philosophy |access-date=7 January 2021}}</ref> [[Property (philosophy)#Categoricalism vs. dispositionalism|Categoricalism]] is the thesis that on a fundamental level there are only categorical properties, that dispositional properties are either non-existent or dependent on categorical properties. [[Property (philosophy)#Categoricalism vs. dispositionalism|Dispositionalism]] is the opposite theory, giving ontological primacy to dispositional properties.<ref name="Kriegel">{{cite journal |last=Kriegel |first=Uriah |title=Introverted Metaphysics: How We Get Our Grip on the Ultimate Nature of Objects, Properties, and Causation |journal=Metaphilosophy |date=2019 |volume=50 |issue=5 |pages=688–707 |doi=10.1111/meta.12391 |s2cid=211938090 |url=https://philpapers.org/rec/KRIIMH}}</ref><ref name="Choi"/> Between these two extremes, there are dualists who allow both categorical and dispositional properties in their ontology.<ref name="Orilia"/> ''Relations'' are ways in which things, the relata, stand to each other.<ref name="Borchert2"/><ref>{{cite book |last=Honderich |first=Ted |title=The Oxford Companion to Philosophy |date=2005 |publisher=Oxford University Press |url=https://philpapers.org/rec/HONTOC-2 |chapter=relations}}</ref> Relations are in many ways similar to properties in that both characterize the things they apply to. Properties are sometimes treated as a special case of relations involving only one relatum.<ref name="Orilia"/> Central for ontology is the distinction between ''internal'' and ''external'' relations.<ref name="MacBride">{{cite web |last=MacBride |first=Fraser |title=Relations |url=https://plato.stanford.edu/entries/relations/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=9 January 2021 |date=2020}}</ref> A relation is ''internal'' if it is fully determined by the features of its relata.<ref>{{cite book |last=Honderich |first=Ted |title=The Oxford Companion to Philosophy |date=2005 |publisher=Oxford University Press |url=https://philpapers.org/rec/HONTOC-2 |chapter=relations, the nature of}}</ref> For example, an apple and a tomato stand in the ''internal relation'' of [[Similarity (philosophy)|similarity]] to each other because they are both red.<ref>{{cite web |last=Allen |first=Sophie |title=Properties |url=https://iep.utm.edu/properties/ |website=Internet Encyclopedia of Philosophy |access-date=19 January 2021}}</ref> Some philosophers have inferred from this that internal relations do not have a proper ontological status since they can be reduced to intrinsic properties.<ref name="MacBride"/><ref>{{cite book |last=Borchert |first=Donald |title=Macmillan Encyclopedia of Philosophy, 2nd Edition |date=2006 |publisher=Macmillan |url=https://philpapers.org/rec/BORMEO |chapter=Relations, Internal and External}}</ref> ''External'' relations, on the other hand, are not fixed by the features of their relata. For example, a book stands in an ''external'' relation to a table by lying on top of it. But this is not determined by the book's or the table's features like their color, their shape, and so forth.<ref name="MacBride"/> === States of affairs and events === [[State of affairs (philosophy)|States of affairs]] are complex entities, in contrast to substances and properties, which are usually conceived as simple.<ref name="Borchert2"/><ref>{{cite book |last=Meinertsen |first=Bo R. |title=Metaphysics of States of Affairs: Truthmaking, Universals, and a Farewell to Bradley's Regress |year=2018 |publisher=Springer Singapore |page=1 |url=https://philpapers.org/rec/MEIMOS-2}}</ref> Complex entities are built up from or constituted by other entities. Atomic states of affairs are constituted by one particular and one property exemplified by this particular.<ref name="Sandkühler2"/><ref name="Textor">{{cite web |last=Textor |first=Mark |title=States of Affairs |url=https://plato.stanford.edu/entries/states-of-affairs/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=9 January 2021 |date=2020}}</ref> For example, the state of affairs that Socrates is wise is constituted by the particular "Socrates" and the property "wise". Relational states of affairs involve several particulars and a relation connecting them. States of affairs that ''obtain'' are also referred to as [[Fact#In philosophy|facts]].<ref name="Textor"/> It is controversial which ontological status should be ascribed to states of affairs that do not obtain.<ref name="Sandkühler2"/> States of affairs have been prominent in 20th-century ontology as various theories were proposed to describe the world as composed of states of affairs.<ref name="Borchert2"/><ref>{{cite book |last1=Wittgenstein |first1=Ludwig |last2=Colombo |first2=G. C. M. |last3=Russell |first3=Bertrand |title=Tractatus Logico-Philosophicus |date=1922 |publisher=[[Fratelli Bocca]] |url=https://philpapers.org/rec/WITTL-14}}</ref><ref>{{cite book |last=Armstrong |first=D. M. |title=A World of States of Affairs |date=1996 |publisher=Cambridge University Press |url=https://philpapers.org/rec/ARMAWO-3}}</ref> It is often held that states of affairs play the role of [[truthmaker]]s: judgments or assertions are true because the corresponding state of affairs obtains.<ref name="Textor"/><ref>{{cite web |last=Asay |first=Jamin |title=Truthmaker Theory |url=https://iep.utm.edu/truth-ma/ |website=Internet Encyclopedia of Philosophy |access-date=9 January 2021}}</ref> [[Event (philosophy)|Events]] take place in time, they are sometimes thought of as involving a change in the form of acquiring or losing a property, like the lawn's becoming dry.<ref name="Honderich2"/> But on a liberal view, the retaining of a property without any change may also count as an event, e.g., the lawn's staying wet.<ref name="Honderich2">{{cite book |last=Honderich |first=Ted |title=The Oxford Companion to Philosophy |date=2005 |publisher=Oxford University Press |url=https://philpapers.org/rec/HONTOC-2 |chapter=events}}</ref><ref name="Kim2"/> Some philosophers see events as universals that can repeat at different times, but the more dominant view is that events are particulars and therefore non-repeatable.<ref name="Kim2">{{cite book |last1=Kim |first1=Jaegwon |last2=Sosa |first2=Ernest |last3=Rosenkrantz |first3=Gary S. |title=A Companion to Metaphysics |publisher=Wiley-Blackwell |url=https://philpapers.org/rec/KIMACT-9 |chapter=event theory|year=1994 }}</ref> Some events are complex in that they are composed of a sequence of events, often referred to as a process.<ref>{{cite book |last=Craig |first=Edward |title=Routledge Encyclopedia of Philosophy |date=1996 |publisher=Routledge |url=https://philpapers.org/rec/BEAREO |chapter=processes}}</ref> But even simple events can be conceived as complex entities involving an object, a time and the property exemplified by the object at this time.<ref>{{cite book |last=Audi |first=Robert |title=The Cambridge Dictionary of Philosophy |publisher=Cambridge University Press |url=https://philpapers.org/rec/AUDTCD-2 |chapter=event|year=1999 }}</ref><ref>{{cite web |last=Schneider |first=Susan |title=Events |url=https://iep.utm.edu/events/ |website=Internet Encyclopedia of Philosophy}}</ref> So-called [[process philosophy]] or [[process ontology]] ascribes ontological primacy to changes and processes as opposed to the emphasis on static being in the traditionally dominant substance metaphysics.<ref>{{cite web |last=Seibt |first=Johanna |title=Process Philosophy |url=https://plato.stanford.edu/entries/process-philosophy/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=9 January 2021 |date=2020}}</ref><ref>{{cite web |last=Hustwit |first=J. R. |title=Process Philosophy |url=https://iep.utm.edu/processp/ |website=Internet Encyclopedia of Philosophy |access-date=9 January 2021}}</ref> ===Reality of things=== The word 'real' is derived from the Latin word ''res'', which is often translated as 'thing'. The word 'thing' is often used in ontological discourse as if it had a presupposed meaning, not needing an explicit philosophical definition because it belongs to ordinary language. Nevertheless, what is a thing and what is real or substantial are concerns of ontology.<ref name="Erices"/><ref>Thomasson, A. L. (2007). ''Ordinary Objects'', Oxford University Press, New York, {{ISBN|978-0195319910}}, p. 7: "I argue that while there are various ways of addressing questions about what 'things' exist, ..."</ref><ref>{{cite book |last=Sandkühler |first=Hans Jörg |url=https://meiner.de/enzyklopadie-philosophie.html |title=Enzyklopädie Philosophie |date=2010 |publisher=Meiner |language=de |section=Zweifel, methodischer: 2 Zur Begriffs- und Problemgeschichte. ›reale Dinge (entia realia)‹ |access-date=2020-12-16 |archive-url=https://web.archive.org/web/20210311040207/https://meiner.de/enzyklopadie-philosophie.html |archive-date=2021-03-11 |url-status=dead}}</ref><ref>Eddington, A.S. (1928). ''The Nature of the Physical World: The Gifford Lectures 1927'', Macmillan, London, England and New York, reprinted 1929 p. ix: "... it is the distinctive characteristic of a "thing" to have this substantiality".</ref><ref name="Isham"/> Different views are held about this. Plato proposed that underlying – and constituting the real basis of – the concretely experienced world are '[[Theory of forms|forms]]' or 'ideas', which today are generally regarded as high abstractions. In earlier days, philosophers used the term '[[Platonic realism|realism]]' to refer to Plato's belief that his 'forms' are 'real'; nowadays, the term 'realism' often has an almost opposite meaning, so that Plato's belief is sometimes called '[[idealism]]'.<ref>Hale, B. (2009). "Realism and antirealism about abstract entities", pp. 65–73 in Jaegwon Kim, Ernest Sosa, and Gary S. Rosenkrantz, ''A Companion to Metaphysics'', 2nd ed., Wiley–Blackwell, Chichester, UK, {{ISBN|978-1405152983}}.1.</ref> Philosophers debate whether entities such as tables and chairs, lions and tigers, philosophical doctrines, numbers, truth, and beauty, are to be regarded as 'things', or as something or nothing 'real'. 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