Consider, first, the application of the method on its psychologi cal side, as it appears in Locke. Starting with the assumption of conscious experience as the content of the individual mind, Locke proceeds to explain its genesis and nature by reference to the real universe of things and its mechanical operation upon the mind. The result of the interaction of mind, i.e., the individual mind, and the system of things, is conscious experience, consisting of ideas, which may be variously compounded, divided, compared, or dealt with by the subjective faculties with which the entity, mind, is supposed to be endowed. Matter of fact and matter of knowledge are thus at a stroke dissevered. The very notion of relation between mind and things leads at once to the counter notion of the absolute restriction of mind to its own subjective nature. That Locke was unable to reconcile these opposed notions is not surprising; that the difficulties and obscurities of the Essay arise from the impossibility of reconciling them is evident on the slightest consideration of the main positions of that work. Of these difficulties the philosophies of Berkeley and Hume are sys tematic treatments. In Berkeley we find the resolute determina tion to accept only the one notion, that of mind as restricted to its own experience, and to attempt by this means to explain the nature of the external reality to which obscure reference is made. Any success in the attempt is due only to the fact that Berkeley introduces alongside of his individualist notion a totally new con ception, that of mind itself as capable of reflection upon the whole of experience and of reference to the supreme mind as the ground of all reality.
It is only in Hume that we have definitely and completely the evolution of the individualist notion as groundwork of a theory of knowledge ; and it is in his writings, therefore, that we may expect to find the fundamental difficulty of that notion clearly apparent. It is not a little remarkable that we should find in Hume, not only the sceptical dissolution of all fixity of cognition, which is the in evitable result of the individualist method, but also the clearest consciousness of the very root of the difficulty. The systematic application of the doctrine that conscious experience consists only of isolated objects of knowledge, impressions or ideas, leads Hume to distinguish between truths reached by analysis and truths which involve real connection of the objects of knowledge. The first he is willing to accept without further inquiry, though it is an error to suppose, as Kant seems to have supposed, that he regarded mathematical propositions as coming under this head (see HUME) ; with respect to the second, he finds himself hope lessly at fault. No real connections between isolated objects of experience are perceived by us. No single matter of fact neces sarily implies the existence of any other. In short, if the diffi culty be put in its ultimate form, no existence can transcend itself, or imply relation to any other existence. If the parts of con scious experience are regarded as distinct things, there is no possi bility of connecting them other than contingently, if at all. If the individual mind be really thought of as individual, it is impossible to explain how it should have knowledge at all. "In short," says
Hume, "there are two principles which I cannot render con sistent, nor is it in my power to renounce either of them, viz., that all our distinct perceptions are distinct existences, and that the mind never perceives any real connection among distinct existences. Did our perceptions either inhere in something simple or indi vidual, or did the mind perceive some real connection among them, there would be no difficulty in the case" (App. to Treatise of Human Nature).
Thus, on the one hand, the individualist conception leads to the total negation of all real cognition. If the real system of things, to which conscious experience has reference, be regarded as standing in casual relation to this experience there is no con ceivable ground for the extension to reality of the notions which somehow are involved in thought. The same result is apparent, on the other hand, when we consider the theory of knowledge implied in the Leibnizian individualism. The metaphysical con ception of the monads, each of which is the universe in nuce, pre sents insuperable difficulties when the connection of the monads is in question, and these difficulties obtrude themselves when the attempt is made to work out a consistent doctrine of cognition. For the whole mass of cognizable fact is contained impliciter in each monad, and the several modes of apprehension can only be regarded as so many stages in the developing monad. Sense and understanding, real connection of facts and analysis of notions, therefore, differ only in degree. The same fundamental axioms, the logical principles of identity and sufficient reason, are applic able in explanation of all given propositions. It is true that Leibniz himself did not work out any complete doctrine of knowl edge, but in the hands of his successors the theory took definite shape in the principle that the whole work of cognition is in essence analytical. The process of analysis might be complete or incomplete. For finite intelligences there was an inevitable incompleteness so far as knowledge of matters of fact was con cerned. In respect to them, the final result was found in a series of irreducible notions or categories, the analysis and elucidation of which was specifically the business of philosophy.
It will be observed that, in the Leibnizian as in the empirical individualism, the fundamental notion is still that of the abstract separation of the thinking subject from the materials of conscious experience. From this separation arise all the difficulties in the effort to develop the notion systematically, and in tracing the his tory of Kant's philosophical progress we are able to discern the gradual perception on his part that here was to be found the ulti mate cause of the perplexities which became apparent in consider ing the subordinate doctrines of the system. The successive essays composing Kant's precritical work are not so many imperfect sketches of the doctrines of the Kritik. They are essentially tenta tive, and exhibit the manner in which the difficulties of a received theory force on a more comprehensive view.