 Once he has established that justice, like the other crafts and virtues, is an other-directed form of practical reason aimed at non-zero-sum goods, Socrates turns to consider its nature and powers more directly. Injustice, he argues, is by nature a cause of disunity, strife, and, therefore, disempowerment and ineffectiveness (351a–352b). Even a gang of thieves can only function successfully when they are just amongst themselves. Likewise within the human soul: justice is what harmonizes the soul and makes a person effective. At this point Thrasymachus more or less gives up on the discussion, but Socrates adds a fifth argument as the coup de grace (352d–354c): justice, as the virtue of the soul (here deploying the conclusion of the third argument), is what enables the soul to perform its functions well, so that the just person lives well and happily. This final argument is a close ancestor of the famous ‘function argument’ used by Aristotle in Nicomachean Ethics I.7: it shows that Plato (and for that matter Aristotle) by no means rejects the Homeric ‘functional’ conception of virtue as such. Rather, the whole argument of the Republic amounts to a proof that it can be reconciled with the demands of Hesiodic justice, if only we understand rightly what successful human functioning consists in. 