In Book II of Plato's Republic, Glaucon locates justice "among the finest goods, as something to be valued […] both because of itself and because of what comes from it."1 Unhappy with the Socratic defence of this doctrine in Book I, Glaucon confronts it with stringent criticism, one element of which is the famous thought-experiment of Gyges' ring, which grants invisibility and so the option of undetectable crime.