Kant's problem is not, in its wording, very different from that which Locke set before him when he resolved to "inquire into the original, certainty and extent of human knowledge together with the grounds and degrees of belief, opinion and assent." Locke's Essay is undoubtedly, in its intention, a contribution to the theory of knowledge. But, because time had not yet made the matter clear, Locke suffered himself to digress in his second book into the psychological question of the origin of our ideas ; and his theory of knowledge is ruined by the failure to distinguish be tween the epistemological sense of "idea" as significant content and the psychological sense in which it is applied to a fact or process in the individual mind. The same confusion runs through Berkeley's arguments and vitiates his conclusions as well as those of Hume. But appearing with these thinkers as the problem of perception, epistemology widens its scope and becomes, in Kant's hands, the question of the possibility of experience in general. With Hegel it passes into a completely articulated "logic," which apparently claims to be at the same time an ontology or an ultimate expression of the nature of the real.
This introduces us to the second part of the question we are seeking to determine, namely the relation of epistemology to ontology. It is evident that philosophy as theory of knowledge must have for its complement philosophy as ontology or theory of being. The question of the truth of our knowledge, and the ques tion of the ultimate nature of what we know, are in reality two sides of the same inquiry; and therefore our epistemological re sults have to be ontologically expressed. But it is not every thinker that can see his way with Hegel to assert in set terms the identity of thought and being. Hence the theory of knowledge becomes with some a theory of human ignorance. This is the case with Herbert Spencer's doctrine of the Unknowable, which he advances as the result of epistemological considerations in the philosophical prolegomena to his system. Very similar positions were maintained by Kant and Comte; and, under the name of "agnosticism" (q.v.), the theory has popularized itself in the outer courts of philosophy, and on the shifting borderland of philosophy and literature. The truth is that the habit of thinking exclusively from the standpoint of the theory of knowledge tends to beget an undue subjectivity of temper. And the fact that it has become usual for men to think from this standpoint is very plainly seen in the almost universal description of philosophy as an analysis of "experience," instead of its more old-fashioned designation as an inquiry into "the nature of things." As it is matter of universal agreement that the problem of being must be attacked indirectly through the problem of knowledge, this substitution may be re garded as an advance, more especially as it implies that the fact of experience, or of self-conscious existence, is the chief fact to be dealt with. But if so, then self-consciousness must be treated
as itself real, and as organically related to the rest of existence. If self-consciousness be treated in this objective fashion, then we pass naturally from epistemology to ontology. (For, although the term "ontology" has been as good as disused, it still remains true that the aim of philosophy must be to furnish us with an ontology or a coherent and adequate theory of the nature of reality.) But if, on the other hand, knowledge and reality be ab initio opposed to one another—if consciousness be set on one side as over against reality, and merely holding up a mirror to it—then it follows with equal naturalness that the truly real must be something which lurks unrevealed behind the subject's representation of it. Hence come the different varieties of a so-called phenomenalism. The upholders of such a theory would, in general, deride the term "ontology"; but it is evident, none the less, that their position itself implies a certain theoiy of the universe and of our own place in it, and the establishment of this theory constitutes their ontology.
Without prejudice, then, to the claim of epistemology to con stitute the central philosophic discipline, we may simply note its liability to be pressed too far. The exclusive preoccupation of men's minds with the question of knowledge during the neo Kantian revival in the 'seventies of the last century drew from Lotze the caustic criticism that "the continual sharpening of the knife becomes tiresome, if after all, we have nothing to cut with it." Stillingfleet's complaint against Locke was that he was "one of the gentlemen of this new way of reasoning that have almost discarded substance out of the reasonable part of the world." The same may be said with greater truth of the devotees of the theory of knowledge; they seem to have no need of so old fashioned a commodity as reality. Yet, after all, Fichte's dictum holds good that knowledge as knowledge—i.e., so long as it is looked at as knowledge—is, ipso facto, not reality. The result of the foregoing, however, is to show that, as soon as epistemology draws its conclusion, it becomes ontology; the theory of knowl edge passes into a theory of being. The ontological conclusion, moreover, is not to be regarded as something added by an external process; it is an immediate implication. The ontology is the epistemology from another point of view—regarded as completing itself, and explaining in the course of its exposition that relative or practical separation of the individual knower from the knowable world, which it is a sheer assumption to take as absolute. This, not the so-called assumption of the implicit unity of being and thought, is the really unwarrantable postulate ; for it is an assumption which we are obliged to retract bit by bit, while the other offers the whole doctrine of knowledge as its voucher.