The aim of this paper is to identify the meaning of Aristotle's natural law (φνσικον δικαιον) in Nicomachean Ethics, Book V, verifying your nonfoundationalist model. Thus, I use, too, some passages in Politics (Pol.), Rhetoric (Ret.) and spurious Magna Moralia (MM). I want to show a unit about the role of natural law in Aristotle's ethics, verifying if the fairness or reasonableness (επιεικεια) it can be understood as what is the correct one.