In this essay the author proposes a heuristic archaeology of the concept of ‘impact’ of norms. If this term was first introduced by Lawrence Friedman, the corresponding concept is not new to legal sociologists. Its archaeology makes it possible to discover some unexpected and interesting socio-legal applications, and it is in this sense that Fittipaldi regards the archaeology presented here as a heuristic one. In the second part, Fittipaldi elaborates on the sociological fruitfulness of a concept first introduced by Amedeo G. Conte: nomotropism (of actions). This concept is complementary to that of impact. Fittipaldi shows its fruitfulness both for sociology of law and other sociologies. Finally, he summarizes the results of this study presenting the set-theoretical relations between impact (referred to with the Contean term "praxeotropism" in order to stress its complementarity with nomotropism), effectiveness, and ineffectiveness - all understood as qualities of norms -, on the one hand, and the set-theoretical relations between nomotropism, compliance, and noncompliance - all understood as qualities of behaviours -, on the other.
Keywords: Impact - Lawrence Friedman - Amedeo G. Conte - Praxeotropism - Anankasticconstitutive rules - Nomotropism