ONTOLOGY. — From the Greek *ón* and *lòyòs*, meaning "science of being," ontology is synonymous with metaphysics (v.) and appears to have been introduced for the first time by J. CLAUBERG, JOHANN (v.), who used the two terms "ontosophia vel o." However, it was popularized especially by C. Wolff (v.) through his work *Philosophia prima sive o. methodo scientifica pertractata qua omnis cognitionis humanae principia continentur* (1730). In § 1, it is defined as: "Scientia entis in genere seu quatenus ens est." After deploring the discredit into which ontology had fallen due to the Scholastics, Wolff promised to rehabilitate it: "Nos eandem a contemptu quo laborat vindicamus, sterili tractatione in foecundam conversa" (new ed., Frankfurt and Leipzig 1736, p. 1). This new terminology passed unchallenged into modern rationalism until the end of the 18th century, when, after Kant (who still preferred the old term "metaphysics"), philosophy, under the influence of idealism, became the theory of the development of the spirit. It reappeared, however, among some secondary thinkers and regained favor in France and Italy with ontologism (v.). While Wolff defined ontology as the science of formal concepts concerning being, the ontologists considered it as the science of reality itself as it is in itself in its absolute source, as seen in Gioberti and Mamiani.
Among the precursors of Neoscholasticism (Sordi), the term "metaphysics" still prevailed, but with an important modification that would have significant influence and likely originated earlier. Metaphysics encompasses the consideration of real being in its broadest extension and is divided into general metaphysics or properly ontology, and special metaphysics, which includes what Aristotle and St. Thomas referred to as "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, definiti potest illa metaphysicae pars quae agit de ente in communi" (D. Sordi, *O.*, ed. by P. Dezza, Milan 1941, p. 39). This new classification frequently recurs among Neoscholastics (Remer, De Maria, Pesch, Frick, De Mandato, Zigliara), including recent ones (Maquart, *Metaphysica ostensiva: ontologia, theologia naturalis*). The term ontology was revived by Husserl to denote the science that studies the essential (eidetic) structures proper to various sciences; thus, Husserl speaks of "regional ontologies," since every positive or empirical science (*Tatsachenwissenschaft*, *Erfahrungswissenschaft*) has its theoretical foundations in eidetic ontologies. He distinguishes a twofold class of material and formal ontologies, depending on whether they consider content or its laws (cf. *Ideen zu einer reinen Phänomenologie*, I, new ed., The Hague 1950, § 9-10, p. 23 ff.). For Heidegger, ontology must investigate the most profound structure of being, unlike the "ontic" research 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 ontology), considers the "foundation," i.e., "being itself" (*Sein selbst*) in its original openness (cf. *Was ist Metaphysik*, 5th ed., Frankfurt 1949, p. 17 ff.). An ontology constructed on the "principle of immanence" is that of G. Jacoby (*Allgemeine Ontologie der Wirklichkeit*, I, Halle 1925), while N. Hartmann reverted to the ancient term "metaphysics" for the analysis of knowledge (*Grundlegung einer Metaphysik der Erkenntnis*, 3rd ed., Berlin 1941).