But then, since for morality I need nothing more than that freedom should not contradict itself, that it should at least be thinkable that it should place no hindrance in the way of the mechanism of nature in the same action (taken in another relation), without it being necessary for me to have any further insight into it: the doctrine of morality asserts its place and the doctrine of nature its own, which, however, would not have oc curred if criticism had not first taught us of our unavoidable ignorance in respect of the things in themselves and limited everything that we can cognize theoretically to mere appearances.