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( on, ontos , being, and logos , science, the science or philosophy of being).


Though the term is used in this literal meaning by Clauberg (1625-1665) (Opp., p. 281), its special application to the first department of metaphysics was made by Christian von Wolff (1679-1754) (Philos. nat., sec. 73). Prior to this time "the science of being" had retained the titles given it by its founder Aristotle : "first philosophy ", "theology", "wisdom". The term " metaphysics " (q.v.) was given a wider extension by Wolff, who divided "real philosophy " into general metaphysics, which he called ontology, and special, under which he included cosmology, psychology, and theodicy. This programme has been adopted with little variation by most Catholic philosophers. The subject-matter of ontology is usually arranged thus:

  • The objective concept of being in its widest range, as embracing the actual and potential, is first analyzed, the problems concerned with essence (nature) and existence, "act" and "potency" are discussed, and the primary principles -- contradiction, identity, etc. -- are shown to emerge from the concept of entity.
  • The properties coextensive with being -- unity, truth, and goodness, and their immediately associated concepts, order and beauty -- are next explained.
  • The fundamental divisions of being into the finite and the infinite, the contingent and the necessary, etc., and the subdivisions of the finite into the categories (q.v.) substance and its accidents (quantity, quality, etc.) follow in turn -- the objective -- reality of substance, the meaning of personality, the relation of accidents to substance being the most prominent topics.
  • The concluding portion of ontology is usually devoted to the concept of cause and its primary divisions -- efficient and final, material and formal --the objectivity and analytical character of the principle of causality receiving most attention.
  • Ontology is not a subjective science as Kant describes it (Ub. d. Fortschr. d. Met., 98) nor "an inferential Psychology ", as Hamilton regards it (Metaphysics, Lect. VII); nor yet a knowledge of the absolute (theology); nor of some ultimate reality whether conceived as matter or as spirit, which Monists suppose to underlie and produce individual real beings and their manifestations. Ontology is a fundamental interpretation of the ultimate constituents of the world of experience. All these constituents -- individuals with their attributes -- have factors or aspects in common. The atom and the molecule of matter, the plant, the animal, man, and God agree in this that each is a being, has a characteristic essence, an individual unity, truth, goodness, is a substance and ( God excepted) has accidents, and is or may be a cause. All these common attributes demand definition and explanation -- definition not of their mere names, but analysis of the real object which the mind abstracts and reflectively considers. Ontology is therefore the fundamental science since it studies the basal constituents and the principles presupposed by the special sciences. All the other parts of philosophy, cosmology, psychology, theodicy, ethics, even logic, rest on the foundation laid by ontology. The physical sciences -- physics, chemistry, biology, mathematics likewise, presuppose the same foundations. Nevertheless ontology is dependent in the order of analysis, though not in the order of synthesis, on these departments of knowledge ; it starts from their data and uses their information in clarifying their presuppositions and principles. Ontology is accused of dealing with the merely abstract. But all science is of the abstract, the universal, not of the concrete and individual. The physical sciences abstract the various phenomena from their individual subjects; the mathematical sciences abstract the quantity -- number and dimensions -- from its setting. Ontology finally abstracts what is left -- the essence, existence, substance, causalty, etc. It is idle to say that of these ultimate abstractions we can have no distinct knowledge. The very negation of their knowableness shows that the mind has some knowledge of that which it attempts to deny. Ontology simply endeavours to make that rudimentary knowledge more distinct and complete. There is a thoroughly developed ontology in every course of Catholic philosophy ; and to its ontology that philosophy owes its definiteness and stability, while the lack of an ontology in other systems explains their vagueness and instability.


    It was Aristotle who first constructed a well-defined and developed ontology. In his "Metaphysics" he analyses the simplest elements to which the mind reduces the world of reality. The medieval philosophers make his writings the groundwork of their commentaries in which they not only expand and illustrate the thought, but often correct and enrich it in the light of Revelation. Notable instances are St. Thomas Aquinas and Francisco Suárez (1548-1617). The "Disputationes Metaphysicae" of the latter is the most thorough work on ontology in any language. The Aristotelean writings and the Scholastic commentaries are its groundwork and largely its substance ; but it amplifies and enriches both. The work of Father Harper mentioned below attempts to render it available for English readers. The author's untimely death, however, left the attempt far from its prospected ending. The movement of the mind towards the physical sciences -- which was largely stimulated and accelerated by Bacon -- carried philosophy away from the more abstract truth. Locke, Hume, and their followers denied the reality of the object of ontology. We can know nothing, they held, of the essence of things; substance is a mental figment, accidents are subjective aspects of an unknowable noumenon; cause is a name for a sequence of phenomena. These negations have been emphasized by Comte, Huxley, and Spencer.

    On the other hand the subjective and psychological tendencies of Descartes and his followers dimmed yet more the vision for metaphysical truth. Primary notions and principles were held to be either forms innate in the mind or results of its development, but which do not express objective reality. Kant, analysing the structure of the cognitive faculties -- perception, judgment, reasoning -- discovers in them innate forms that present to reflection aspects of phenomena which appear to be the objective realities, being, substance, cause, etc., but which in truth are only subjective views evoked by sensory stimuli. The subject matter of Ontology is thus reduced to the types which the mind, until checked by criticism, projects into the external world. Between these two extremes of Empiricism and Idealism the traditional philosophy retains the convictions of common sense and the subtle analysis of the Scholastics. Being, essence, truth, substance, accident, cause, and the rest, are words expressing ideas but standing for realities. These realities are objective aspects of the individuals that strike the senses and the intellect. They exist concretely outside of the mind, not, of course, abstractly as they are within. They are the ultimate elementary notes or forms which the mind intuitively discerns, abstracts, and reflectively analyses in its endeavour to comprehend fundamentally any object. In this reflective analysis it must employ whatever information it can obtain from empirical psychology. Until recently this latter auxiliary has been insufficiently recognized by the philosophers. The works, however, of Maher and Walker mentioned below manifest a just appreciation of the importance of psychology's cooperation in the study of ontology.

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