The article deals with the problem of modal inference: if some addressees are
obliged to do something, they are also obliged to realize states of affairs which
constitute a necessary condition for the main obligation. Likewise, they are obliged
to refrain from realizing states of affairs which constitute a sufficient condition for
the action contradicting the main obligation. This type of inference is called in Polish legal theory “instrumental inference”. It is argued in the article that sometimes instrumental norms in law must be fulfilled (“preparatory actions” must be undertaken) before the main obligation is fulfilled. Lawgiver helps addressees of norms by applying vacatio legis. It can lead to new paradoxical consequences – to the creation of “virtual norms” – norms which never come into force, but addressees are obliged to undertake preparatory actions. The article presents theoretical
description of this phenomenon. In conclusion one dogmatic claim is proposed:
there is a potential way (art. 4171 § 1 k.c.) of getting from public officials compensation for preparatory actions which caused burden for addressees, when the main obligation turned out to be “virtual”. In Poland this procedure should be based on the rulings of the Constitutional Tribunal.