According to Mises, the strictly universal sentences of economics can be legitimated logically and epistemologically. Praxeology allegedly provides an a priori true theory of human action. Several aspects of the precise content of the a priori true fundamental axiom "Man acts' and of the additional, empirical auxiliary axioms are explicated. To act involves to employ means in order to attain ends. Idiosyncratically, all actions are rational on Mises' account. Finally, three issues of Mises' praxeology are discussed, which are often neglected or denied otherwise: Mises' fallibilism, the necessary and challenging combination of praxeology with thymology in explanations, and Mises' interest in empirical questions.