All the other parts of philosophy, cosmology, psychology, theodicy, ethics, even logic, rest on the foundation laid by ontology. Ontology is accused of dealing with the merely abstract. But all science is of the abstract, the universal, not of the concrete and individual. 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.
It was Aristotle who first constructed a well-defined and developed ontology. 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. 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. Locke, Hume, and their followers denied the reality of the object of ontology.