From the acceptance of such a definition two important consequences would follow. (1) The first is that metaphysics is at once sharply discriminated from any study of the psychical _process_ of knowledge, if indeed, there can be any such study distinct from the psychology of conception and belief, which is clearly not itself the science we have in view. For the psychological laws of the formation of concepts and beliefs are exemplified equally in the discovery and propagation of truth and of error. And thus it is in vain to look to them for any explanation of the difference between the two. Nor does the otherwise promising extension of Darwinian conceptions of the "struggle for existence" and the "survival of the fittest" to the field of opinions and convictions appear to affect this conclusion. Such considerations may indeed assist us to understand how true convictions in virtue of their "usefulness" gradually come to be established and extended, but they require to presume the truth of these convictions as an antecedent condition of their "usefulness" and consequent establishment. I should infer, then, that it is a mistake in principle to seek to replace ontology by a "theory of knowledge," and should even be inclined to question the very possibility of such a theory as distinct from metaphysics on the one hand and empirical psychology on the other. (2) The second consequence is of even greater importance. The inquiry into the general character by which the contents of true assertions are discriminated from the contents of false assertions must be carefully distinguished from any investigation into the truth or falsehood of special assertions. To ask how in the end truth differs from falsehood is to raise an entirely different problem from that created by asking whether a given statement is to be regarded as true or false. The distinction becomes particularly important when we have to deal with what Locke would call assertions of "real existence," _i. e._, assertions as to the occurrence of particular events in the temporal order. All such assertions depend, in part at least, upon the admission of what we may style "empirical" evidence, the immediate unanalyzed witness of simple apprehension to the occurrence of an alleged matter of fact. Thus it would follow from our proposed conception of metaphysics that metaphysics is in principle incapable either of establishing or refuting any assertion as to the details of our immediate experience of empirical fact, though it may have important bearings upon any theory of the general nature of true Being which we may seek to found upon our alleged experiences. In a word, if our conception be the correct one, the functions of a science of metaphysics in respect of our knowledge of the temporal sequence of events psychical and physical must be purely critical, never constructive,--a point to which I shall presently have to recur.