Kelsen’s two basic ideas on legal interpertation are, on the one hand, its characterisation as a hybrid with both cognitive and volitive elements, due to the partial indetermination of law; and, on the other hand, the relationship between legal interpretation and the structural properties of the legal system (dynamic principle). Kelsen’s solution to the problem of irregular norms –the so-called “tacit alternative clause”– not only raises the accusation of decisionism, but also seems to displace the question of norm content and, therefore, legal interpretation to an irrelevant place within his theory of law. I will argue that a less irracionalist reconstruction of Kelsen’s thesis is possible starting from his initial intuition on legal interpretation. This reconstruction is based on two arguments: (i) the distinction between the validity of a norm and the fact that the act by which it is created is a correct interpretation of the higher norm, that is, a non-reductionist concept of validity; (ii) a funtional interpretation (that has a hobbesian background) of the “determination” of the norm content between the different hierarchical levels of the legal system.