Is the just person truly happier than the unjust person? In his comparative thesis, Plato never directly addresses what happiness is, but by analyzing certain definitions that are provided throughout the Republic and fleshing out the relations between those definitions, one can come to a clearer understanding of what he meant when he referred to happiness. The pivotal definitions are those of Justice, Wisdom, and Pleasure. The interplay between these shows a picture of happiness that is perhaps more fully formed than the reader may suppose at first glance. Justice is the dominant component of happiness, and must be present in order for it to be possible. And Justice is not sustainable without Wisdom; therefore happiness (as a stable state) cannot be reached without it either. Wisdom is gained through engaging in and experiencing the highest and truest Pleasures, which are rational ones. This involves being of a philosophic nature and studying the Forms, which are unchanging and present in everything. Through this kind of study, one is able to inform the ruling part of the soul most reliably, make better decisions about which pleasures would be the most appropriate for each part of the soul, and therefore maintain justice most consistently within the soul. That established, happiness will be most possible for this kind of person.

Justice, according to Plato, is a soul’s virtue. It is equivalent to a kind of psychic harmony, or deep peace, in which each part of the soul performs its own task well and does not meddle in the affairs of other parts or do their work (444 b). The three parts of the soul are the appetitive, the spirited, and the rational parts, having to do (respectively) with bodily pleasures and desires; anger, envy, and righteous indignation; and reason and knowledge. The psychic harmony of the just soul is beautifully described when Socrates says that “one who is just…
“… regulates well what is really his own and rules himself. He… harmonizes the three parts of himself like three limiting notes in a musical scale— high, low, and middle. He binds together those parts and any others there may be in between, and from having been many things he becomes entirely one, moderate and harmonious. Only then does he act” (443 d-e).

When these three parts are working together in harmony as they should, the rational part rules over both the appetitive part and the spirited part with its knowledge, reigning them in and keeping them in line, as it were, for the good of the whole soul.

The choice of the rational part of the soul as ruler may seem arbitrary and unfounded until one understands why Plato laid out the criterion for the just city first. Once one sees the explicit parallel made between the just city and the just individual, it is easy to follow the reasoning whereby each of the four virtues previously outlined for the city can be brought down and applied on an individual level. Thus, wisdom is the knowledge of what is best for each part and for the whole soul, courage is the preservation of beliefs about what is to be feared and what isn’t, and moderation is the agreement between the three parts of the soul that the rational part should rule. Justice as well is applied to the individual level when Socrates says:
“I suppose we’ll say that a man is just in the same way as a city?… And we surely haven’t forgotten that the city was just because each of the three classes in it was doing its own work… Then we also must remember that each one of us in whom each part is doing its own work will himself be just and do his own… Therefore, isn’t it appropriate for the rational part to rule, since it is really wise and exercises foresight on behalf of the whole soul, and for the spirited part to obey and be its ally?” (441d-e).

This is where Wisdom makes its entrance. The kingship of the rational part of the soul is shown to be appropriate when the speakers agree that, “everything… that has to do with virtue [is] the same in both [the city and the individual]”(441d). In each case, Wisdom reigns supreme in the sense that both the philosopher-king and the rational part of the soul are uniquely able to gain, and rely on, true knowledge in order to make their judgements.
Justice is not maintainable without wisdom, because the continued harmonious relations between the parts of the soul are made more and more possible to the extent that the rational part is informed by Wisdom. To understand this, looking at the individual, it helps to refer back to Plato’s description of how the philosophic nature manifests itself: we see that
“ the philosophic natures always love the sort of learning that makes clear to them some feature of the being that always is and does not wander around between coming to be and decaying” (485b), and that “it is the nature of the real lover of learning to struggle toward what is… until he grasps the being of each nature itself with the part of his soul that is fitted to grasp it.” (490b, emphasis mine).

‘What is’ and ‘what always is’ as referred to here are the Forms: things that are unchanging and present in everything. Knowledge of this kind is true knowledge, gained through contemplation of the Forms, and is naturally gained by the philosophic nature. Filling oneself with this knowledge will reliably inform the rational part of the soul with wisdom and understanding, bringing the potential for a consistently maintained state of psychic harmony (or justice), and therefore, for happiness. The more one meditates on the Forms and ‘what is’, the more just one’s soul will be since the ruling part will be making the wisest decisions about the which Pleasures are most appropriate for each part of the soul.

In the Republic, Plato contradicts the popular notion that pain is the absence of pleasure and pleasure the absence of pain.
“Is it any surprise, then, …that when [the many] descend into the painful, they believe truly and are really in pain, but that, when they ascend from the painful to the intermediate state, they firmly believe that they have reached fulfilment and pleasure?” (584e-585).

He says that the masses are deceived into believing that their relief from pain is pleasure, mindlessly accepting it as such without really analyzing it. What they hold to be pleasure is really the neutral absence of pain, however, and there is a pleasure higher yet. This true pleasure comes from filling ourselves with “what is appropriate to our nature… with things that are more, [thereby enjoying] more really and truly a more true pleasure” (585e).
Maintaining a state of psychic harmony, or justice, will allow one to lead the pleasurable life; without justice, true pleasure and happiness are impossible. Justice is the largest component of happiness, and therefore, when present, allows for the greatest possibility of being happy. It is not a guarantee, however. It is possible for one to be just and unhappy as well. Though it is the dominant element of happiness and a necessary condition for it, justice is not a sufficient condition for it. There are external conditions over which one has no authority, and sometimes, no matter how much virtue one may possess internally, happiness is not to be found. This can be seen in the case of a just soul under torture. There seems to be a mysterious lesser ingredient in happiness that sort of drowns in the wake of the argument at hand and remains unaddressed. However, the Plato has established that justice is a necessary but not sufficient condition for happiness.

In conclusion, Plato says that Justice is necessary in order to experience true pleasure and ultimately happiness. This is because only when each part of the soul minds its own business and harmonizes with the other parts is conflict going to cease so one can experience peace and pleasure. And only when the rational part of the soul is ruling do you see and act on what is best for each part of the soul and the whole, because only it chooses the rational pleasures (the truest pleasures) above mere bodily pleasures and honor and the rest. The rational part of the soul chooses to study the Forms and gain true knowledge of that which is unchanging (Wisdom) in order to make its decisions. As ruler, then, it makes the wisest judgements about the best Pleasures for each part of the soul, thereby preserving justice within the soul

Real Pleasure comes from ‘filling ourselves with what is appropriate to our nature’ (585e), thereby informing our soul’s rational part with Wisdom on what kinds of decisions will preserve the substantial foundation of Justice within the soul, making Happiness possible, if not entirely guaranteed. When justice is preserved and made to be a consistent state, then we can potentially be happy more consistently (excluding external effects like the torture mentioned before) and therefore the philosophic soul that is just is the one with the most potential to be happy and fulfilled.

c. Mary Kathryn Gough, university paper

(Katie Huffman (Gough, married), History of Philosophy I, Van Dyke 251 A)