Reasonableness is a complex concept that is used both in legal and in political theory. Its complexity depends on its variety of dimensions that range between epistemology and ethics, law and politics. Rather than aiming only at a conceptual analysis, I believe that a semantic inquiry into judicial uses can not only help to clarify the variety of meanings usually attributed to reasonableness—both in civil law and in common law, both in public and private law—but also serves as a necessary point of reference with regard to a normative theory of reasonableness. I attempt here to gesture toward a ‘philosophy of reasonableness’ that, inspired by Von Wright’s appeal to Aristotle, aims at proposing an understanding of the concept different from Rawls’s ‘public reason’ and more attuned to the variety of uses of the notion in contemporary society. Reasonableness, I hold, cannot simply be reduced to a value akin to impartiality and equality, as Rawls and Alexy would have it, because it is a concept that encompasses ‘the right way of living’. It expresses an ethical view that can be grasped in its complexity only by also focusing on the elements of its structure and their functioning.