Plato’s great work of the middle period, the Republic, is devoted to answering a challenge made by the sophist Thrasymachus, that conventional morality, particularly the ‘virtue’ of justice, actually prevents the strong man from achieving eudaimonia. Thrasymachus’s views are restatements of a position which Plato discusses earlier on in his writings, in the Gorgias, through the mouthpiece of Callicles. The basic argument presented by Thrasymachus and Callicles is that justice (being just) hinders or prevents the achievement of eudaimonia because conventional morality requires that we control ourselves and hence live with un-satiated desires. This idea is vividly illustrated in book 2 of the Republic when Glaucon, taking up Thrasymachus’ challenge, recounts a myth of the magical ring of Gyges. According to the myth, Gyges becomes king of Lydia when he stumbles upon a magical ring, which, when he turns it a particular way, makes him invisible, so that he can satisfy any desire he wishes without fear of punishment. When he discovers the power of the ring he kills the king, marries his wife and takes over the throne.[8] The thrust of Glaucon’s challenge is that no one would be just if he could escape the retribution he would normally encounter for fulfilling his desires at whim. But if eudaimonia is to be achieved through the satisfaction of desire, whereas being just or acting justly requires suppression of desire, then it is not in the interests of the strong man to act according to the dictates of conventional morality. (This general line of argument reoccurs much later in the philosophy of Nietzsche.) Throughout the rest of the Republic, Plato aims to refute this claim by showing that the virtue of justice is necessary for eudaimonia.
The argument of the Republic is lengthy and complex. In brief, Plato argues that virtues are states of the soul, and that the just person is someone whose soul is ordered and harmonious, with all its parts functioning properly to the person’s benefit. In contrast, Plato argues that the unjust man’s soul, without the virtues, is chaotic and at war with itself, so that even if he were able to satisfy most of his desires, his lack of inner harmony and unity thwart any chance he has of achieving eudaimonia. Plato’s ethical theory is eudaimonistic because it maintains that eudaimonia depends on virtue. On Plato’s version of the relationship, virtue is depicted as the most crucial and the dominant constituent of eudaimonia.[9]
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