Über drei Deduktionen in Kants Moralphilosophie - und über eine vierte, die man dort vergeblich sucht. Zur Rehabilitierung von Grundlegung III

Abstract:Since H. J. Paton’s famous commentary from 1947, Kant’s interpreters have considered a ‘deduction of the categorical imperative’ a challenge. This is quite puzzling since Kant himself never talks about such a deduction - and the famous ‘deduction’ he does mention in Groundwork III.4 is, as a close reading shows, not at all the deduction of a law but the deduction of a concept, of the idea of a pure lawgiving will: Only the reality of this idea can explain the possibility of - prima facie impossible - categorical imperatives and thus of morality as autonomy. The presupposition of the validity of the moral law, however, was already a cornerstone of Kant’s critical metaphysics in 1781: Moral theology (which replaces all speculative proofs of immortality and of God’s existence) depends on the moral law’s being an undisputed datum without any need for philosophical justification (‘deduction’). While in the Groundwork (1785) Kant tried to show the practical reality of the idea of a pure will with the help of a speculative deduction of freedom (which a reviewer described as being ‘uncritical’ in May 1786), in the second Critique (1787/88) the reality of that very idea, and with it the idea of freedom, depends (as did immortality and God’s existence in 1781) on the aforementioned practical datum, which, from that point on, Kant called a “Factum der reinen Vernunft” [fact of pure reason].