Contemporary discussions about practical reason or practical rationality invoke four competing views which can be named as follows by reference to their historical models: Aristotelian, Hobbesian, Kantian and Nietzschean. The subject-matter of this article is a defence of the Kantian conception of practical rationality in the interpretation of discourse theory. At the heart, lies the justification and the application of the rules of discourse. An argument consisting of three parts is pre sented to justify the rules of discourse. The three (...) parts are as follows: a transcen dental-pragmatic argument; an argument which takes account of the maximisation of individual utility and an empirical premise about an interest in correctness. Within the framework of the problem of application, the article outlines a justification of human rights and of the basic institutions of the democratic constitutional state on the basis of discourse theory. (shrink)