ONTOLOGIA. – From ὄν and λόγος, the science of being; metaphysics (v.) and seems to have been introduced for the first time by J. CLAUBERG, JOHANN (v.), who used the two terms « ontosophia vel o. », but it was disseminated above all by Cr. Wolff (v.), through the work Philosophia prima sive o. methodo scientifica pertractata qua omnis cognitionis humanae principia continentur (1730). In § 1 it is defined: « Scientia entis in genere seu quatenus ens est »; and Wolff, after deploring the discredit into which o. had fallen through the fault of the Scholastics, promises to rehabilitate it: « Nos eandem a contemptu quo laborat vindicamus, sterili tractatione in foecundam conversa » (new ed., Frankfurt and Leipzig 1736, p. 1). The new terminology passed unchallenged in modern rationalism until the end of the 18th century, when, after Kant (who nevertheless still preferred the old term metaphysics), philosophy became, through the work of idealism, the theory of the development of the spirit. It reappears, however, among certain thinkers of secondary importance and returns to favor ontologism (v.). But whereas Wolff defined o. as the science of formal concepts concerning being, the ontologists regard it as the science of reality itself as it is in itself, in its absolute source, as do Gioberti and Mamiani.
Among the precursors of neo-Scholasticism (Sordi), the term « metaphysics » still prevailed, but with an important modification that would gain wide acceptance and probably goes back to an earlier origin. Metaphysics embraces the consideration of real being in its broadest extension and is divided into a general metaphysics, or properly o., and a special metaphysics, which embraces what for Aristotle and St. Thomas was « natural philosophy », dealing with the nature of bodies (cosmology) and the nature of living beings, including man (psychology): « O., quae a greco nomine desumpta latine idem est ac sermo de ente, definiri potest illa metaphysicae pars quae agit de ente in communi » (D. Sordi, O., ed. by P. Dezza, Milan 1941, p. 39). The new classification occurs frequently among the neo-Scholastics (Remer, De Maria, Pesch, Frick, De Mandato, Zigliara), including more recent ones (Maquart, Metaphysica ostensiva: ontologia, theologia naturalis). The term o. was taken up again by Husserl to indicate the science that studies the essential (eidetic) structures proper to the various sciences; hence Husserl speaks of « regional o. », insofar as every positive or experimental science (Tatsachenwissenschaft, Erfahrungswissenschaft) has its theoretical foundations in eidetic o., and distinguishes a twofold class of material and formal o., according as they consider the content or its laws (cf. Ideen zu einer reinen Phänomenologie, I, new ed., The Hague 1950, § 9–10, p. 23 ff.). For Heidegger, o. must investigate the deepest structure of being, in contrast to the « ontic » inquiry proper to the sciences (cf. Sein und Zeit, I, 5th ed., Halle 1941, § 3, p. 11). In his later writings Heidegger proposes a Fundamentalontologie which, instead of stopping at « being as being » (traditional o.), considers the « foundation », that is, « being itself » (Sein selbst) in its original openness (cf. Was ist Metaphysik, 5th ed., Frankfurt 1849, p. 17 ff.). An o. constructed in accordance with the « principle of immanence » is that of G. Jacoby (Allgemeine Ontologie der Wirklichkeit, I, Halle 1925), whereas N. Hartmann returned to the ancient term « metaphysics »
also for the analysis of knowing (Grundlegung einer Metaphysik der Erkenntnis, 3rd ed., Berlin 1941).