The present essay is a partial discussion of what I regard as the central problem of epistemology. In order that its drift may be clearly seen from the outset, I will begin by explaining briefly—without argument—my view of Philosophy, Epistemology and their relation. I take it to be the business of Philosophy—in Mr. Spencer’s words—to “unify” or systematise as completely as possible our common thought, which it finds partially systematised in a number of different sciences and studies. Now before attempting this unification, we must wish to be somehow assured that the thoughts or beliefs which we seek to systematise completely are true and valid. This is obvious; no rational being with his eyes open would try to work up a mixture of truth and error into a coherent system, without some attempt to eliminate the error.
It is primâ facie necessary, therefore, as a preliminary to the task of bringing into—or exhibiting in—coherent relation the different bodies of systematic thought which furnish the matter for Philosophy, to have some criteria for distinguishing truth from error. It may, however, be thought that this need—though undeniably urgent in the case of such studies as, e.g., Politics and Theology—will not be practically presented, so long as the philosopher’s work is confined to the positive sciences. The prevalence of error in Politics is kept prominently before our minds by the system of party government; and the effective working of this system almost requires the conviction on either side that the political programme of the other party—unhappily often in a majority—is a tissue of errors. So again in Theology, it is the established belief of average members of any religious denomination that the whole world outside the pale of the denomination lies in the darkness of error on some fundamental points; and even within the pale, the wide-spread existence of right-hand backslidings and left-hand defections from the standard of orthodoxy is con-
