Abstract
The old division of all sciences into the two equally important classes of theoretical and practical disciplines is hardly ever applied today. However, the proprium of a practical science that is aimed at what should be, can be elucidated using medicine as an example. The efforts of medicine are not limited to a mere `application' of methods and results of theoretical disciplines. Even the concepts of `illness' and `diagnosis', which are central to medicine, are defined in a normative-deontological manner. They are supposed not only to help formulating and justifying assertions on facts, but also to be a means to enable and standardise action. Since every action takes place in a concrete situation, a practical science must always bridge the hiatus between the general and the particular. This requires judgement, a personal, individual capacity that cannot be operationalised without residue. In contrast to the theoretical disciplines, such a science is not the master of its own questions and problems; and is subject to the dictate of time, since all action is final and irrevocable