The systematic relevance of the arguments Schopenhauer directs against Kant's categorical imperative has hardly been discussed in detail so far. As the difference between Kant's and Schopenhauer's moral philosophy amounts to the opposition between practical reason and sympathy, it is anything but surprising that it is reflected by Schopenhauer's objections. Schopenhauer tries to show is that practical reason be it in its pure or empirical form is altogether incapable of furnishing a solid basis for ethics. To assess the import of this thesis, a detailed examination of the aspects of practical reason that provoke Schopenhauer's critique is necessary including: 1) the identification of morality and reason; 2) the moral value of maxims; 3) the categorical imperative; 4) the prescriptive character of Kant's approach; and 5) his ethicotheology. Although some of Schopenhauer's arguments are based on misunderstanding, his interpretation of the categorical imperative as an expression of rational egoism seems convincing.