The author reviews different possible meanings of the notion of “reasonableness of the law”. He analyses the main thesis on reasonableness of the so-called neocostituzionalismo (neo-constitutionalism), focusing on the relationship between this thesis and the rule of law as a limit to arbitrary power. He discusses the theory of the reasonable balancing of principles as a way to take the “correct decision” in a judicial case as well as the theory of legal argumentation in relation to the problem of flexibility in decision-making. In conclusion, the author discusses the relationship between neo-constitutionalism and cognitivist thesis in meta-ethics.