THIS IS a book of acquaintance. As a rule, college students and general readers have had little or no acquaintance with ontology, or general metaphysics, as a science in its own right. Many ideas of an ontological or metaphysical character are, of course, encountered in their daily reading in books, magazine articles, scientific treatises, and professional discussions of all kinds. While the general meaning of such ideas is clear enough, their signification and implication, as an integral part in the structure of philosophic thought, is unknown or hardly felt. They become understood and appreciated in their full value only when studied in the context of the philosophic science of ontology or metaphysics as a whole. Hence the need of correlating these scattered ideas into a basic science, such as ontology, and of fitting them into the fundamental framework of a philosophic system of thought.In accordance with this purpose, the scope of the book is frankly positive and constructive. It attempts to build up an understanding of the matter of ontology in a logical manner, using simple language, illustrating the subjects with copious examples, and extracting the contents of each chapter into compact summaries. Some of the more abstruse problems of ontology, such as the problem of essence and existence, have been omitted; it was felt that the average student would derive little benefit from a lengthy discussion of problems which have taxed the ingenuity and acumen of the most profound intellects. Such problems may be attacked after the student has become acquainted with the ideas and subjects which form the foundation of the science of metaphysics. After all, the student cannot be expected to be a professional philosopher; it should be sufficient if he acquires a thorough grounding in fundamentals, so that he can deepen his knowledge through subsequent reading and study.