Ontology

=== Ancient Greek ===
[[File:Parmenides.jpg|thumb|upright|[[Parmenides]] was among the first to propose an ontological characterization of the fundamental nature of reality.]]
In the [[Ancient Greek philosophy|Greek philosophical tradition]], [[Parmenides]] was among the first to propose an ontological characterization of the fundamental nature of existence. In the prologue (or [[Parmenides#Introduction|''proem'']]) to ''On Nature'', he describes two views of [[existence]]. Initially, nothing comes from nothing, thus [[existence]] is [[Monism|eternal]]. This posits that existence is what may be conceived of by thought, created, or possessed. Hence, there may be neither void nor vacuum, and true reality may neither come into being nor vanish from existence. Rather, the entirety of creation is eternal, uniform, and immutable, though not infinite (Parmenides characterized its shape as that of a perfect sphere). Parmenides thus posits that change, as perceived in everyday experience, is illusory.

Opposite to the [[Eleatics|Eleatic]] [[monism]] of [[Parmenides]] is the [[Pluralism (philosophy)|pluralistic]] conception of [[being]]. In the 5th century BCE, [[Anaxagoras]] and [[Leucippus]] replaced<ref>{{Cite book |last=Graham |first=Daniel W. |url=https://press.princeton.edu/books/hardcover/9780691125404/explaining-the-cosmos |title=Explaining the Cosmos |date=2006-08-06 |publisher=Princeton University Press |isbn=978-0-691-12540-4 |language=en}}</ref> the reality of ''being'' (unique and unchanging) with that of [[Becoming (philosophy)|''becoming'']], therefore by a more fundamental and elementary ''ontic'' plurality. This thesis originated in the [[Hellenic world]], stated in two different ways by Anaxagoras and by Leucippus. The first theory dealt with "seeds" (which Aristotle referred to as "''homeomeries''") of the various substances. The second was the [[Atom (order theory)|atomistic]] theory,<ref>{{cite web |url= http://plato.stanford.edu/entries/atomism-ancient/ | title= Ancient Atomism (Stanford Encyclopedia of Philosophy) | publisher= Plato.stanford.edu | access-date= 2010-02-21}}</ref> which dealt with reality as based on the [[vacuum]], the atoms and their intrinsic movement in it.<ref>Lloyd, G. E. R. (2006). Leucippus and Democritus. In D. M. Borchert (Ed.), ''Encyclopedia of philosophy'' (2nd ed., Vol. 5, pp. 297–303). Macmillan Reference USA.</ref>

The materialist ''[[atomism]]'' proposed by Leucippus was [[indeterminism|indeterminist]], but [[Democritus]] ({{c.}} 460 – {{c.}} 370 BCE) subsequently developed it in a [[deterministic]] way. Later (4th century BCE), [[Epicurus]] took the original ''atomism'' again as indeterministic. He saw reality as composed of an infinity of indivisible, unchangeable corpuscles, or [[atom]]s (from the Greek ''atomon'', lit. 'uncuttable'), but he gives weight to characterize atoms, whereas for Leucippus they are characterized by a "figure", an "order", and a "position" in the cosmos.<ref>Aristotle, ''Metaphysics'', I, 4, p. 985.</ref> Atoms are, besides, creating the whole with the intrinsic movement in the ''vacuum'', producing the diverse flux of being. Their movement is influenced by the ''parenklisis'' ([[Lucretius]] names it ''[[clinamen]]'') and that is determined by [[Randomness|chance]]. These ideas foreshadowed the understanding of traditional [[physics]] until the advent of 20th-century theories on the nature of atoms.<ref>
{{cite book |url=https://books.google.com/books?id=j5YEviKRlyIC |title=Contributions to Social Ontology |publisher=Routledge |year=2007 |isbn=978-1136016066 |editor1-last=Lawson |editor1-first=Clive |series=Routledge Studies in Critical Realism |location=London |publication-date=2013 |access-date=3 March 2019 |editor2-last=Latsis |editor2-first=John Spiro |editor3-last=Martins |editor3-first=Nuno}}
</ref>{{page needed|date=March 2019}}

[[Plato]] developed the distinction between true reality and illusion, in arguing that what is real are eternal and unchanging [[Theory of Forms|forms]] or ideas (a precursor to [[universal (metaphysics)|''universals'']]), of which things experienced in sensation are at best merely copies, and real only in so far as they copy ("partake of") such forms. In general, Plato presumes that all nouns (e.g., "beauty") refer to real entities, whether sensible bodies or insensible forms. Hence, in [[Sophist (dialogue)|''The Sophist'']], Plato argues that ''being'' is a ''form'' in which all existent things participate and which they have in common (though it is unclear whether "being" is intended in the sense of [[existence]], [[copula (linguistics)|copula]], or [[identity (philosophy)|identity]]); and argues, against [[Parmenides]], that forms must exist not only of ''being'', but also of [[negation]] and of non-being (or ''difference'').{{citation needed |date= September 2017}}

In his [[Categories (Aristotle)|''Categories'']], Aristotle (384–322 BCE) identifies ten possible kinds of things that may be the subject or the predicate of a proposition. For Aristotle there are four different ontological dimensions:<ref>{{Cite encyclopedia |last=Studtmann |first=Paul |date=2007-09-07 |title=Aristotle's Categories |encyclopedia=Stanford Encyclopedia of Philosophy |url=https://stanford.library.sydney.edu.au/entries/aristotle-categories/#FouFolDiv}}</ref>

# according to the various categories or ways of addressing a being as such
# according to its truth or falsity (e.g., fake gold, counterfeit money)
# whether it exists in and of itself or simply 'comes along' by accident
# according to its potency, movement (energy) or finished presence ([[Metaphysics (Aristotle)|''Metaphysics'' Book Theta]]).