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Originally Latin ontologia (1606, Ogdoas Scholastica, by Jacob Lorhard (Lorhardus)), from Ancient Greek ὤν ‎(ṓn, on), present participle of εἰμί ‎(eimí, being, existing, essence) + λόγος ‎(lógos, account).

First known English use 1663: Archelogia philosophica nova; or, New principles of Philosophy. Containing Philosophy in general, Metaphysicks or Ontology, Dynamilogy or a Discourse of Power, Religio Philosophi or Natural Theology, Physicks or Natural philosophy, by Gideon Harvey (1636/7-1702), London, Thomson, 1663.

Popularized as a philosophical term by German philosopher Christian Wolff (1679–1754).


ontology ‎(plural ontologies)

  1. (uncountable, philosophy) The branch of metaphysics that addresses the nature or essential characteristics of being and of things that exist; the study of being qua being.
  2. (countable, philosophy) The theory of a particular philosopher or school of thought concerning the fundamental types of entity in the universe.
    • 2000, C. D. C. Reeve, Substantial Knowledge: Aristotle's Metaphysics, Hackett Publishing, p. 97:
      The answer to the controversial question of whether Aristotle's ontology includes non-substantial particulars, then, is that it does.
  3. (logic) A logical system involving theory of classes, developed by Stanislaw Lesniewski (1886-1939).
  4. (computer science, information science) A structure of concepts or entities within a domain, organized by relationships; a system model.

Usage notes[edit]

In the field of philosophy there is some variation in how the term ontology is used. Ontology is a much more recent term than metaphysics and takes its root meaning explicitly from the Greek term for being. Ontology can be used loosely as a rough equivalent to metaphysics or more precisely to denote that subset of the domain of metaphysics which is focused rigorously on the study of being as being.


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  • ontology” in An American Dictionary of the English Language, by Noah Webster, 1828.
  • ontology in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913
  • ontology” in Dictionary.com Unabridged, v1.0.1, Lexico Publishing Group, 2006.
  • ontology” in Microsoft's Encarta World English Dictionary, North American Edition (2007)
  • ontology” in the Compact Oxford English Dictionary (Oxford University Press, 2007)
  • "ontology" by F.P. Siegfried, in The Catholic Encyclopedia (Robert Appleton Company, New York, 1911)
  • Oxford English Dictionary, second edition (1989)
  • Random House Webster's Unabridged Electronic Dictionary (1987-1996)
  • Dictionary of Philosophy, Dagobert D. Runes (editor), Philosophical Library (1962); see: "Ontology" by James K. Feibleman, page 219
  • "Ontology" by Tom Gruber to appear in the Encyclopedia of Database Systems, Ling Liu and M. Tamer Özsu (editors), Springer-Verlag (2008)