I. REASON OF INTRODUCTORY CHAPTER.—It is desirable that at some stage in the course of his investigations the student of philosophy should be invited to take a brief general survey of the work in which he is engaged. This purpose will be served by a chapter on _the general aim and scope of philosophy_, its distinctive characteristics as compared with other lines of human thought, and its relations to these latter. Such considerations will at the same time help to define _Ontology_, thus introducing the reader to the subject-matter of the present volume. II. PHILOSOPHY: THE NAME AND THE THING.—In the fifth book of Cicero’s _Tusculan Disputations_ we read that the terms _philosophus_ and _philosophia_ were first employed by Pythagoras who flourished in the sixth century before Christ, that this ancient sage was modest enough to call himself not a “wise man” but a “lover of wisdom” (φίλος, σοφία), and his calling not a profession of wisdom but a search for wisdom. However, despite the disclaimer, the term _philosophy_ soon came to signify _wisdom_ simply, meaning by this the highest and most precious kind of knowledge. Now human knowledge has for its object everything that falls in any way within human experience. It has _extensively_ a great variety in its subject-matter, and _intensively_ a great variety in its degrees of depth and clearness and perfection. _Individual facts_ of the past, communicated by human testimony, form the raw materials of _historical_ knowledge. Then there are all the individual things and events that fall within one’s own personal experience. Moreover, by the study of human language (or languages), of works of the human mind and products of human genius and skill, we gain a knowledge of _literature_, and of the _arts_—the fine arts and the mechanical arts. But not merely do we use our senses and memory thus to accumulate an unassorted stock of informations about isolated facts: a miscellaneous mass of mental furniture which constitutes the bulk of human knowledge in its _least developed_ form—_cognitio ____vulgaris,___ the knowledge of the comparatively uneducated and unreflecting classes of mankind. We also use our reasoning faculty to reflect, compare, classify these informations, to interpret them, to reason about them, to infer from them _general truths_ that embrace individual things and events _beyond our personal experience_; we try to explain them by seeking out their _reasons_ and _causes_. This mental activity gradually converts our knowledge into _scientific_ knowledge, and thus gives rise to those great groups of systematized truths called the _sciences_: as, for example, the physical and mathematical sciences, the elements of which usually form part of our early education. These sciences teach us a great deal about ourselves and the universe in which we live. There is no need to dwell on the precious services conferred upon mankind by discoveries due to the progress of the various _special_ sciences: