The principles of reasonableness and proportionality are not per se suitable for establishing a “what ought to beµ. However, they can provide lawyers with a tool for the consistency check over the outcome of the hermeneutic activity. On the contrary, the principle of effectiveness has a preceptive content that identifies a new kind of legality, as envisaged by all the Constitutions of the twentieth century, as well as the European Treaties. The process of building the foundations of a sustainable society requires lawyer to combine legality and effectiveness, to recover his role as a source of law and contribute to overcome the old-fashion dialectic on the priority of the Law, on the one side, against the priority of the Judges, on the other side