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! === Medieval === Medieval ontology was strongly influenced by Aristotle's teachings. The thinkers of this period often relied on Aristotelian categories like ''substance'', ''act and potency'', or ''matter and form'' to formulate their own theories. Important ontologists in this epoch include Avicenna, Thomas Aquinas, [[Duns Scotus]], and [[William of Ockham]].<ref>{{cite web |last1=Gracia |first1=Jorge |last2=Newton |first2=Lloyd |title=Medieval Theories of the Categories |url=https://plato.stanford.edu/entries/medieval-categories/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=1 January 2021 |date=2016}}</ref><ref>{{cite web |last=Brower |first=Jeffrey |title=Medieval Theories of Relations |url=https://plato.stanford.edu/entries/relations-medieval/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=1 January 2021 |date=2018}}</ref><ref name="Dahlstrom"/> According to [[Avicenna]]'s interpretation of Greek Aristotelian and Platonist ontological doctrines in medieval [[metaphysics]], being is either necessary, contingent ''qua'' possible, or impossible. Necessary being is that which cannot but be, since its non-being would entail a contradiction. Contingent ''qua'' possible being is neither necessary nor impossible for it to be or not to be. It is ontologically neutral, and is brought from potential existing into actual existence by way of a cause that is external to its essence. Its being is borrowed—unlike the necessary existent, which is self-subsisting and impossible not to be. As for the impossible, it necessarily does not exist, and the affirmation of its being would involve a contradiction.<ref> [[Nader El-Bizri]], '[[Ibn Sina]] and [[Essentialism]], Review of [[Metaphysics]], Vol. 54 (2001), pp. 753–778. </ref> Fundamental to [[Thomas Aquinas]]'s ontology is his distinction between [[essence]] and [[existence]]: all entities are conceived as composites of essence and existence.<ref name="Kerr">{{cite web |last=Kerr |first=Gaven |title=Aquinas: Metaphysics |url=https://iep.utm.edu/aq-meta/ |website=Internet Encyclopedia of Philosophy |access-date=18 December 2020}}</ref><ref>{{cite web |last=Brown |first=Christopher M. |title=Thomas Aquinas |url=https://iep.utm.edu/aquinas/ |website=Internet Encyclopedia of Philosophy |access-date=18 December 2020}}</ref><ref>{{cite web |last=Magee |first=Joseph |title=Ontology |url=https://aquinasonline.com/ontology/ |website=Thomistic Philosophy Page |access-date=18 December 2020 |language=en |date=9 February 2020}}</ref> The essence of a thing is what this thing is like, it signifies the definition of this thing.<ref>{{cite web |last=Magee |first=Joseph |title=Essence and Existence |url=https://aquinasonline.com/essence-and-existence/ |website=Thomistic Philosophy Page |access-date=18 December 2020 |language=en |date=4 February 2020}}</ref> God has a special status since He is the only entity whose essence is identical to its existence. But for all other, finite entities there is a ''real distinction'' between essence and existence.<ref>{{cite book |last=Craig |first=Edward |title=Routledge Encyclopedia of Philosophy |date=1996 |publisher=Routledge |url=https://philpapers.org/rec/BEAREO |chapter=Aquinas, Thomas}}</ref> This distinction shows itself, for example, in our ability to understand the essence of something without knowing about its existence.<ref>{{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=Thomas Aquinas, St.}}</ref> Aquinas conceives of existence as an ''act of being'' that actualizes the potency given by the essence. Different things have different essences, which impose different limits on the corresponding ''act of being''.<ref name="Kerr"/> The paradigm examples of essence-existence composites are material substances like cats or trees. Aquinas incorporates Aristotle's distinction between [[matter and form]] by holding that the essence of ''material'' things, as opposed to the essence of ''immaterial'' things like angels, is the composition of their matter and form.<ref name="Kerr"/><ref>{{cite web |last1=McInerny |first1=Ralph |last2=O'Callaghan |first2=John |title=Saint Thomas Aquinas |url=https://plato.stanford.edu/entries/aquinas/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=18 December 2020 |date=2018}}</ref> So, for example, the essence of a marble statue would be the composition of the marble (its matter) and the shape it has (its form). Form is universal since substances made of different matter can have the same form. The forms of a substance may be divided into substantial and accidental forms. A substance can survive a change of an accidental form, but ceases to exist upon a change of a substantial form.<ref name="Kerr"/> Summary: Please note that all contributions to Christianpedia may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here. You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Christianpedia:Copyrights for details). Do not submit copyrighted work without permission! Cancel Editing help (opens in new window) Discuss this page