Ontology

=== Modern ===
Ontology is increasingly seen as a separate domain of philosophy in the modern period.<ref name="Dahlstrom"/><ref>{{cite book |last=Jaroszyski |first=Piotr |title=Metaphysics or Ontology? |date=2018 |publisher=Brill |url=https://philpapers.org/rec/JARMOO |chapter=Summary of Part 2}}</ref> Many ontological theories of this period were rationalistic in the sense that they saw ontology largely as a deductive discipline that starts from a small set of first principles or axioms, a position best exemplified by Baruch Spinoza and Christian Wolff. This rationalism in metaphysics and ontology was strongly opposed by [[Immanuel Kant]], who insisted that many claims arrived at this way are to be dismissed since they go beyond any possible experience that could justify them.<ref name="Borchert"/><ref name="Sandkühler">{{cite book |last=Sandkühler |first=Hans Jörg |title=Enzyklopädie Philosophie |date=2010 |publisher=Meiner |url=https://meiner.de/enzyklopadie-philosophie.html |chapter=Ontologie: 2 Zur Begriffs- und Problemgeschichte |access-date=2020-12-16 |archive-date=2021-03-11 |archive-url=https://web.archive.org/web/20210311040207/https://meiner.de/enzyklopadie-philosophie.html |url-status=dead }}</ref>

[[René Descartes]]' ontological distinction between mind and body has been one of the most influential parts of his philosophy.<ref name="Sandkühler"/><ref name="Skirry">{{cite web |last=Skirry |first=Justin |title=Descartes, Rene: Mind-Body Distinction |url=https://iep.utm.edu/descmind/ |website=Internet Encyclopedia of Philosophy |access-date=19 December 2020}}</ref> On his view, minds are thinking things while bodies are extended things. ''Thought'' and ''extension'' are two ''attributes'' that each come in various ''modes'' of being. Modes of ''thinking'' include judgments, doubts, volitions, sensations and emotions while the shapes of material things are modes of ''extension''.<ref name="Smith">{{cite web |last=Smith |first=Kurt |title=Descartes' Theory of Ideas |url=https://plato.stanford.edu/entries/descartes-ideas/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |date=2018}}</ref> Modes come with a lower degree of reality since they depend for their existence on a substance.<ref>{{cite journal |last=Nelson |first=Alan |title=Introduction: Descartes's Ontology |journal=Topoi |date=1997 |volume=16 |issue=2 |pages=103–109 |doi=10.1023/A:1005877628327 |s2cid=170986842 |url=https://philpapers.org/rec/NELIDO-3}}</ref> Substances, on the other hand, can exist on their own.<ref name="Smith"/> Descartes' [[substance dualism]] asserts that every finite substance is either a thinking substance or an extended substance.<ref>{{cite journal |last=Rodriguez-Pereyra |first=Gonzalo |title=Descartes's Substance Dualism and His Independence Conception of Substance |journal=Journal of the History of Philosophy |date=2008 |volume=46 |issue=1 |pages=69–89 |doi=10.1353/hph.2008.1827 |s2cid=201736234 |url=https://philpapers.org/rec/RODDSD}}</ref><ref>{{cite web |last=Robinson |first=Howard |title=Dualism |url=https://plato.stanford.edu/entries/dualism/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |date=2020}}</ref> This position does not entail that minds and bodies ''actually are'' separated from each other, which would defy the intuition that we both have a body and a mind. Instead, it implies that minds and bodies ''can'', at least in principle, be separated, since they are distinct substances and therefore are capable of independent existence.<ref name="Skirry"/><ref>{{cite book |last=Craig |first=Edward |title=Routledge Encyclopedia of Philosophy |date=1996 |publisher=Routledge |url=https://philpapers.org/rec/BEAREO |chapter=Descartes, René}}</ref> A longstanding problem for substance dualism since its inception has been to explain how minds and bodies can [[Problem of mental causation|causally interact]] with each other, as they apparently do, when a volition causes an arm to move or when light falling on the retina causes a visual impression.<ref name="Skirry"/>

[[Baruch Spinoza]] is well known for his ''substance monism:'' the thesis that only one substance exists.<ref name="Sandkühler"/><ref name="Dutton">{{cite web |last=Dutton |first=Blake D. |title=Spinoza, Benedict De |url=https://iep.utm.edu/spinoza/ |website=Internet Encyclopedia of Philosophy |access-date=21 December 2020}}</ref> He refers to this substance as "God or Nature", emphasizing both his [[pantheism]] and his [[Naturalism (philosophy)|naturalism]].<ref>{{cite web |last=Mander |first=William |title=Pantheism |url=https://plato.stanford.edu/entries/pantheism/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=21 December 2020 |date=2020}}</ref> This substance has an infinite amount of attributes, which he defines as "what the intellect perceives of substance as constituting its essence".<ref>{{cite web |last=Shein |first=Noa |title=Spinoza's Theory of Attributes |url=https://plato.stanford.edu/entries/spinoza-attributes/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=21 December 2020 |date=2018}}</ref> Of these attributes, only two are accessible to the human mind: thought and extension. ''Modes'' are properties of a substance that follow from its attributes and therefore have only a dependent form of existence.<ref>{{cite book |last=Viljanen |first=Valtteri |title=The Cambridge Companion to Spinoza's Ethics |date=2009 |publisher=Cambridge University Press |url=https://philpapers.org/rec/VILSO |chapter=Spinoza's Ontology|pages=56–78 }}</ref> Spinoza sees everyday-things like rocks, cats or ourselves as mere modes and thereby opposes the traditional [[Aristotle|Aristotelian]] and [[Descartes|Cartesian]] conception of categorizing them as substances.<ref name="Waller">{{cite web |last=Waller |first=Jason |title=Spinoza, Benedict de: Metaphysics |url=https://iep.utm.edu/spinoz-m/ |website=Internet Encyclopedia of Philosophy |access-date=21 December 2020}}</ref> Modes compose [[deterministic]] systems in which the different modes are linked to each other as cause and effect.<ref name="Dutton"/> Each deterministic system corresponds to one attribute: one for extended things, one for thinking things, and so forth. Causal relations only happen within a system while the different systems run in parallel without causally interacting with each other.<ref name="Waller"/> Spinoza calls the system of modes ''Natura naturata'' ("nature natured"), and opposes it to ''Natura naturans'' ("nature naturing"), the attributes responsible for the modes.<ref>{{cite book |last=Craig |first=Edward |title=Routledge Encyclopedia of Philosophy |date=1996 |publisher=Routledge |url=https://philpapers.org/rec/BEAREO |chapter=Spinoza, Benedict de (1632–77)}}</ref> Everything in Spinoza's system is necessary: there are no contingent entities. This is so since the attributes are themselves necessary and since the system of modes follows from them.<ref name="Dutton"/>

[[Christian Wolff (philosopher)|Christian Wolff]] defines ontology as the science of being in general. He sees it as a part of metaphysics besides cosmology, psychology and natural theology.<ref name="Craig">{{cite book |last=Craig |first=Edward |title=Routledge Encyclopedia of Philosophy |date=1996 |publisher=Routledge |url=https://philpapers.org/rec/BEAREO |chapter=Wolff, Christian}}</ref><ref name="Hettche">{{cite web |last1=Hettche |first1=Matt |last2=Dyck |first2=Corey |title=Christian Wolff |url=https://plato.stanford.edu/entries/wolff-christian/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=16 December 2020 |date=2019}}</ref><ref>{{cite book |last=Wolff |first=Christian |title=Preliminary Discourse on Philosophy in General |date=1963 |publisher=Indianapolis: Bobbs-Merrill |pages=45–46 |url=https://philpapers.org/rec/WOLPDO-2}}</ref> According to Wolff, it is a [[deductive]] science, knowable [[a priori|''a priori'']] and based on two fundamental principles: the [[principle of non-contradiction]] ("it cannot happen that the same thing is and is not") and the [[principle of sufficient reason]] ("nothing exists without a sufficient reason for why it exists rather than does not exist").<ref name="Sandkühler"/><ref name="Craig"/> ''Beings'' are defined by their ''determinations'' or ''predicates'', which cannot involve a contradiction. Determinates come in three types: ''essentialia'', ''attributes'', and ''modes''.<ref name="Craig"/> ''Essentialia'' define the nature of a being and are therefore necessary properties of this being. ''Attributes'' are determinations that follow from essentialia and are equally necessary, in contrast to ''modes'', which are merely contingent. Wolff conceives ''existence'' as just one determination among others, which a being may lack.<ref name="Hettche"/> Ontology is interested in being at large, not just in actual being. But all beings, whether actually existing or not, have a sufficient reason.<ref name="Borchert">{{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, History of}}</ref> The sufficient reason for things without actual existence consists in all the determinations that make up the essential nature of this thing. Wolff refers to this as a "reason of being" and contrasts it with a "reason of becoming", which explains why some things have actual existence.<ref name="Hettche"/>

[[Arthur Schopenhauer]] was a proponent of [[Voluntarism (philosophy)#Metaphysical voluntarism|metaphysical voluntarism]]:<ref>{{cite web |title=Voluntarism |url=https://www.britannica.com/topic/voluntarism-philosophy |website=Encyclopedia Britannica |access-date=21 November 2020 |language=en}}</ref> he regards will as the underlying and ultimate reality.<ref>{{cite book |last1=Ortegat |first1=P. |last2=Walker |first2=L. J. |title=New Catholic Encyclopedia Volume 14 |page=582 |url=https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/voluntarism |chapter=Voluntarism}}</ref> Reality as a whole consists only of one will, which is equated with the [[Kantian]] [[thing-in-itself]]. Like the Kantian thing-in-itself, the will exists outside space and time. But, unlike the Kantian thing-in-itself, the will has an experiential component to it: it comes in the form of striving, desiring, feeling, and so forth.<ref>{{cite web |last=Wicks |first=Robert |title=Arthur Schopenhauer |url=https://plato.stanford.edu/entries/schopenhauer/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=21 November 2020 |date=2019}}</ref><ref>{{cite book |last=Young |first=Julian |title=Schopenhauer |date=2005 |publisher=Routledge |url=https://philpapers.org/rec/YOUS |chapter=3. Metaphysics: The World as Will}}</ref> The manifold of things we encounter in our everyday experiences, like trees or cars, are mere appearances that lack existence independent of the observer. Schopenhauer describes them as objectivations of the will. These objectivations happen in different "steps", which correspond to the [[Platonic forms]].<ref>{{cite book |last=Frauenstädt |first=Julius |title=Schopenhauer-Lexikon. Ein Philosophisches Wörterbuch, Nach Arthur Schopenhauers Sämmtlichen Schriften Und Handschriftlichem Nachlass |date=1871 |publisher=F. A. Brockhaus |url=http://www.schopenhauers-kosmos.de/Objektivation |chapter=Objektivation}}</ref> All objectivations are grounded in the will. This grounding is governed by the [[principium individuationis|''principium individuationis'']], which enables a manifold of individual things spread out in space and time to be grounded in the one will.<ref name="Kastrup">{{cite book |last=Kastrup |first=Bernardo |title=Decoding Schopenhauer's Metaphysics: The Key to Understanding How It Solves the Hard Problem of Consciousness and the Paradoxes of Quantum Mechanics |publisher=John Hunt Publishing |isbn=978-1789044270 |url=https://books.google.com/books?id=-jDtDwAAQBAJ |language=en |chapter=10. Individuality and dissociation|year= 2020 }}</ref>