Note 67 — Chapter III · The Ideal of Pure Reason

A conception is always possible, if it is not self-contradictory. This is the logical criterion of possibility, distinguishing the object of such a conception from the nihil negativum. But it may be, notwithstanding, an empty conception, unless the objective reality of this synthesis, but which it is generated, is demonstrated; and a proof of this kind must be based upon principles of possible experience, and not upon the principle of analysis or contradiction. This remark may be serviceable as a warning against concluding, from the possibility of a conception—which is logical—the possibility of a thing—which is real.