It is, however, with regard to the doctrine of pre-established harmony that Kant's large measure of indebtedness to Leibniz is most apt to be overlooked. Kant's claim that Leibniz himself meant the doctrine in a subjective sense (that is, of a harmony between powers in our own intelligence) rather than objective (or between things out of relation to intelligence) seems, at first sight, to go far beyond the mark. However, when we recall that to Leibniz the sense world is only the confused side of rational thought, there is more truth in Kant's saying than appears at this first sight. The harmony is between sense and reason. But it may at least be said without qualification that Kant only translated into subjective terms, terms of intelligence, what appears in Leibniz as objective. This is not the place to go into the details of Kant's conception of the relation of the material to the psychical, of the body and the soul. We may state, however, in his own words, that "the question is no longer as to the possibility of the association of the soul with other known and foreign substances outside it, but as to the connection of the presentations of inner sense with the modifications of our external sensibility." It is a question, in short, of the harmony of two modes of our own presentation, not of the harmony of two independent things. And Kant not only thus deals with the fact of harmony, but he admits, as its _possible_ source, just what Leibniz claims to be its _actual_ source; namely, some one underlying reality, which Leibniz calls the monad, but to which Kant gives no name. "I can well suppose," says Kant, "that the substance to which through external sense extension is attributed, is also the subject of the presentations given to us by its inner sense: _thus that which in one respect is called material being would be in another respect thinking being_."