Abstract

I examine all the occasions on which Aquinas uses a particular example, which goes back to Plato's Republic, to shed light on the controversial subject of the immutability of natural law. Aquinas usually transcribes it as depositum gladius non debet restitui furioso, although some variations also occur. We shall first look at the context in which Plato situates this idea, then go on to examine the occasions on which Aquinas draws on it: in the Summa, when discussing the question as to whether the natural law is the same for everyone; in his Commentary on the Nicomachean Ethics, when he explains in what sense natural law may change, and in what sense it remains the same; and finally, where he examines the virtues of gnome and epieikeia, also in the Summa.