After a short description of the economic model of behaviour first the weak rationality assumption in this model is discussed. As the assumption of self-interest is often seen to be an integral part of the economic model, we also discuss this assumption and its role in economic theorising. Then the two central normative rationality concepts of economics are discussed, which are both based on the Pareto principle: static and dynamic efficiency. It is shown that objections against this approach are hardly convincing. We conclude with some remarks on the relation between economic, legal and political rationality.