According to the theory of truth-functions the truth/falsehood of a proposition is computable from the truth/falsehood of its "internal" propositions: for each (molecular) proposition there is a function (its own function) between truth values. Possible world semantics arises from the application of that theory to modal propositions; modal semantics - the reduction of normative concepts to modal concepts - arises from its application to normative propositions. But the 'paradoxes of deontic logic', as they are called, undermine such reduction: they cannot be seen as mere anomalies but instead as evidence for the wrongness of modal semantics. In all these paradoxes, the necessitation rule, as well as the distribution axiom, fail. Nevertheless, the fulfillment/nonfulfillment of norms (not the truth/falsehood of normative propositions) is computable from the truth/falsehood of the propositions which express the required states of affairs.