(2.) In the _transcendental discussion_ Kant draws his proof indirectly by showing that certain sciences, universally recognized as such, can only be conceived upon the supposition that space and time are apriori. A pure mathematics is only possible on the ground that space and time are pure and not empirical intuitions. Kant comprises the whole problem of the Transcendental Æsthetics in the question—how are pure mathematical sciences possible? The ground, says Kant, upon which pure mathematics moves, is space and time. But now mathematics utters its principles as universal and necessary. Universal and necessary principles, however, can never come from experience; they must have an apriori ground; consequently it is impossible that space and time, out of which mathematics receives its principles, should be first given aposteriori; they must be given apriori as pure intuitions. Hence we have a knowledge apriori, and a science which rests upon apriori grounds; and the matter simply resolves itself into this, viz.: whosoever should deny that apriori knowledge can be, must also at the same time deny the possibility of mathematics. But if the fundamental truths of mathematics are intuitions apriori, we might conclude that there may be also apriori conceptions, out of which, in connection with these pure intuitions, a metaphysics could be formed. This is the positive result of the Transcendental Æsthetics, though with this positive side the negative is closely connected. Intuition or immediate knowledge can be attained by man only through the sensory, whose universal intuitions are only space and time. But since these intuitions of space and time are no objective relations, but only subjective forms, there is therefore something subjective mingled with all our intuitions, and we can know things not as they are in themselves, but only as they appear to us through this subjective medium of space and time. This is the meaning of the Kantian principle, that we do not know things in themselves, but only phenomena. But if on this account we should affirm that all things are in space and time, this would be too much; they are in space and time only for us,—all phenomena of the external sense appearing both in space and in time, and all phenomena of the inner sense appearing only in time. Notwithstanding this, Kant would in no ways have admitted that the world of sense is mere appearance. He affirmed, that while he contended for a transcendental ideality, there was, nevertheless, an empirical reality of space and time: things external to ourselves exist just as certainly as do we and the circumstances within us, only they are not represented to us as they are in themselves and in their independence of space and of time. As to the question, whether there is any thing in the thing itself back of the phenomena, Kant intimates in the first edition of his Critick, that it is not impossible that the Ego and the thing-in-itself are one and the