is to be found in Hobbes. An excellent example of the former is to be found in the writings of Bishop Berkeley[1]. As Hobbes sought to show that the only substance is body, so Berkeley sought to show that the only substance is spirit. The nature of spirit, according to Berkeley, is first and directly known in that knowledge which each man has of himself. Then, in order to account for the independent and excellent order of nature, one must suppose a universal or divine spirit that causes and sustains it, a spirit that is like ourselves in kind, but infinite in power and goodness.
THE THEORY OF KNOWLEDGE
A fourth group of problems that assumes great prominence in the literature of philosophy is called the Theory of Knowledge. Although of all philosophical inquiries this may seem at first glance most artificial and academic, a little reflection will reveal its crucial importance. Suppose, for example, that it is a question of the finality of science, or the legitimacy of faith. The question can be answered only by examining the methods of science in order to discover whether there is anything arbitrary in them that limits the scope of the results. And one must inquire what constitutes genuine knowledge, or when a thing is finally explained, or whether there be things that necessarily lie beyond the reach of human faculties, or whether it be proper to allow aspirations and ideals to affect one's conclusions. Bacon[2] and Descartes,[3] the founders of modern philosophy, devoted themselves primarily to such questions, so that all thought since their time has taken these questions as the point of departure. Furthermore, philosophy has called attention to a very peculiar predicament in which the human thinker finds himself. He seems compelled to begin with himself. When Descartes sought to reduce knowledge to a primal and indubitable certainty he found that certainty to be the knowledge that each thinker has of his own existence, and of the existence of his own ideas. And if a thinker begins with this nucleus, how is he ever to add anything to it; how is he ever to be sure of the existence of anything which is not himself or his ideas ? On the other hand, while my knowledge is most certainly of and within myself, yet it can scarcely be knowl-
