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〖H. C., xxxix, 116, 143.〗 and Descartes,〖H. C., xxxiv, 5.〗 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 knowledge unless it takes me beyond myself. This has become the central difficulty of philosophy. It is a genuine difficulty, and yet everybody neglects it except the philosopher. Berkeley was led by an examination of this difficulty to conclude that if reality is to be assumed to be knowable, then it can be composed of nothing but thinkers and their ideas. And in this conclusion Berkeley has been followed by the whole school of the idealists, the school which has numbered among its members the most eminent thinkers of later times, and has inspired notable movements in German and English literature. Other schools have been led by an examination of the same difficulty to quite different conclusions. But this difficulty has been the crux of modern thought, and no one can hope to debate fundamental issues at all without meeting it.

Such, then, are some of the matters that at once come under discussion when one attempts to think radically and fundamentally. Philosophy is brought to these and like problems because it expresses the profound restlessness of the mind, a dissatisfaction with ready-made, habitual, or conventional opinions, a free and unbounded curiosity, and the need of rounding up the world and judging it for the purposes of life.

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