Now it may seem natural that as soon as one has abandoned the ter rain of experience, one would not immediately erect an edifice with cognitions that one possesses without knowing whence, and on the credit of principles whose origin one does not know, without having first assured oneself of its foundation through careful investigations, thus that one would have long since raised the question how the understanding could come to all these cognitions a priori and what do main, validity, and value they might have.