our faculties. An example of this might perhaps be the conception of a being out of time; such as the proposition: the indestructibility of our true being by death is not a continued existence of it. With conceptions of this sort the firm ground which supports our whole knowledge, the perceptible, seems to waver. Therefore philosophy may certainly at times, and in case of necessity, extend to such knowledge, but it must never begin with it.
The working with wide abstractions, which is condemned above, to the entire neglect of the perceptive knowledge from which they are drawn, and which is therefore their permanent and natural controller, was at all times the principal source of the errors of dogmatic philosophy. A science constructed from the mere comparison of conceptions, that is, from general principles, could only be certain if all its principles were synthetical a priori, as is the case in mathematics: for only such admit of no exceptions. If, on the other hand, the principles have any empirical content, we must keep this constantly at hand, to control the general principles. For no truths which are in any way drawn from experience are ever unconditionally true. They have therefore only an approximately universal validity; for here there is no rule without an exception. If now I link these principles together by means of the intersection of their concept-spheres, one conception might very easily touch the other precisely where the exception lies. But if this happens even only once in the course of a long train of reasoning, the whole structure is loosed from its foundation and moves in the air. If, for example, I say, "The ruminants have no front incisors," and apply this and what follows from it to the camel, it all becomes false, for it only holds good of horned ruminants. What Kant calls das Vernünfteln, mere abstract reasoning, and so often condemns, is just of this sort. For it consists simply in subsuming conceptions under conceptions, without reference to their origin, and without proof of the correctness and exclusive-
