Abstract

This article examines Kant′s use of the expression “fact of reason” by giving an analysis of the pseudo-mathematical method which Kant employs in the first part of the Critique of Practical Reason. It turns out that Kant′s use of this expression has nothing to do with appealing to a certain fact as being an obvious, self-evident truth. There is no need for such an appeal since the “Fundamental Law of Pure Practical Reason” is a “practical postulate” which, like a postulate in geometry, is unquestionably certain. In order to realize its validity it is sufficient to know what a practical law is and on what its validity depends. The fundamental law of pure practical reason needs, in Kant′s view, a “deduction” since it is a synthetic principle a priori. But its deduction cannot be a proof since postulates neither can nor need be proved. It has to be a justification which guarantees that the use of pure reason in giving practical laws is not “transcendent”, but “immanent”. This justification has, unlike Kant′s deduction of the “Postulates of Empirical Thinking”, the systematic form of a “defence” which invalidates possible objections by showing that they themselves necessarily rest on a transcendent use of reason