Glaucon and Adeimantus have been silent, but now that the discussion in Book I has ended unsatisfactorily, they are disappointed with the outcome. Glaucon challenges Socrates not just to drive his interlocutors into contradiction, as he has done thus far, but to demonstrate once and for all that the just life really is better than the unjust life.

Socrates accepts the challenge and tries to meet it in the remaining books of the Republic.

The Search for Justice

To show that the just life is better, Socrates first takes up the question of what justice is (Republic II.368c).

This is what the reader might expect, given his practice in the early dialogues in which he searches for a definition, but now, in the Republic, Socrates proceeds in an unexpected way. He does not search simply for what justice is. Instead, he searches for what justice is in a city and what it is in an individual. He says that he will search for what justice is in a city, because it is "bigger," and so presumably more straightforward to consider, and then, with the nature of justice in the city understood, he will search for what justice is in a human being.

This strategy can seem puzzling, but the Gorgias provides some explanation. Socrates says that when someone "does what is fitting (προσήκοντα) as regards men, his actions will be just (δίκαι᾽)..." (Gorgias 507a). A few lines earlier he says that "when a certain order, the proper (οἰκεῖος) one for each thing, is present, a thing is good" (Gorgias 506e).

Remember also that Thrasymachus demanded that Socrates not explain what justice is by supplying a synonym. A synonym is not informative. He wants Socrates to say what justice is in terms of the underlying facts. "[D]o you yourself answer, Socrates, and tell us what you say the just is. And don't you be telling me that it is that which ought to be, or the beneficial or the profitable or the gainful or the advantageous, but express clearly and precisely whatever you say. For I won't take from you any such drivel as that" (Republic I.336d).

These passages help explain the strategy Socrates pursues in the Republic. The suggestion is that the correct answer to the "What is justice?" question is the relatively uninformative one that justice is what is appropriate with respect to human beings. In the Republic, unlike in the early dialogues, the pursuit of a definition is no longer what drives the discussion. The search is for justice is in a city and in an individual. Socrates begins with the search for justice in the city. This is a search for the proper organization of human beings into cities.

P.Oxy.LII 3679, manuscript from the 3rd century CE, Plato's Republic V.472e-473d. (P.Oxy is the Oxyrhynchus Papyri.
Oxyrhynchus is a city in Egypt situated on a branch of the Nile river, about 185 miles south of Alexandria. The papyri
were in the town dumps, which provided ideal conditions for preservation.)

What Justice is in the City

Human beings organize themselves in cities to make their lives better. Cities provide the benefits of group living, but there are appropriate and inappropriate ways that human beings can organize themselves into a city. The appropriate organizations constitute justice in the city. These organizations function in a certain way.

Socrates says these organizations function so that the city has three parts. It has a guardian, or ruling, class. The rulers are lovers of wisdom (Republic V.473d). They introduce the rules for the production and distribution of goods and for the behavior of individuals in the city more generally. The city also has an auxiliary class. Its job is to enforce the rules. Finally, the city has a working class to produce the services and material goods. The rulers must rule, the auxiliaries must enforce the rules, and the workers must produce the services and material goods.

"I think our city, if it has been rightly (ὀρθῶς) founded, is completely good (τελέως ἀγαθὴν). Clearly, then, it will be wise (σοφή), brave (ἀνδρεία), moderate (σώφρων), and just (δικαία). So if we find any of these qualities in it, the remainder will be that which we have not found" (Republic IV.427e).

Socrates says that this city is wise because the rulers are wise, brave because the auxiliaries are brave, moderate because everyone is controlled, and just because each of three parts does its own job.

"The proper functioning of the working class, the guardians, and the rulers, each doing its own work in the city, ... would be justice (δικαιοσύνη) and would render the city just" (Republic IV.434c-d).

What Justice is in the Individual

Now that they have found justice in the city, they apply their results to justice in an individual human being.

To apply their results to justice in the individual human being, they appeal to a principle about the use of words to call many things by the same name. The idea is that when someone predicates justice of many things-- "this city is just, this human being is just"--, he is saying the same thing each of the many things he calls by the same name.

"If you call a thing by the same name whether it is big or little, it is like in the way in which it is called the same or like. Then a just man too will not differ at all from a just city in respect of the very form of justice, but will be like it (καὶ δίκαιος ἄρα ἀνὴρ δικαίας πόλεως κατ᾽ αὐτὸ τὸ τῆς δικαιοσύνης εἶδος οὐδὲν διοίσει, ἀλλ᾽ ὅμοιος ἔσται). But now the city was thought to be just because three natural kinds existing in it performed each its own function, and again it was temperate, brave, and wise because of certain other affections and habits of these three kinds. Then, my friend, we shall thus expect the individual also to have these same forms in his soul, and by reason of identical affections of these with those in the city to receive properly the same appellations" (Republic IV.435a-c).

Given this principle about the use of words, and give their understanding of justice in the city as the proper organization of the parts of the city,it seems to follow that the soul has parts. Socrates suggests this question of parts is difficult, but he appeals to a principle about opposites (discussed in a previous lecture) to show that the human soul is tripartite.

"The matter begins to be difficult when you ask whether we do all these things with the same thing or whether there are three things and we do one thing with one and one with another--learn (μανθάνομεν) with one part of ourselves, feel anger (θυμούμεθα) with another, and with yet a third desire (ἐπιθυμοῦμεν) the pleasures of nutrition and generation and their kind, or whether it is with the entire soul (ἢ ὅλῃ τῇ ψυχῇ) that we function in each case when we once begin. That is what is really hard to determine properly" (Republic IV.436a-b).

So as justice in the city is the proper organization of human beings into cities, justice in the individual is the proper organization of the parts of his "soul" (ψυχή). The proper organization of these parts is one in which the three parts are in "harmony" (ἁρμονία). In this organization, "reason" (τὸ λογιστικὸν) rules and takes "spirit" (τὸ θυμοειδές) as its ally against "appetite" (τὸ ἐπιθυμητικόν).

"It is fitting for the reasoning part to rule (ἄρχειν), it being wise and exercising foresight on behalf of the whole soul, and for the spirited part to obey it and be its ally" (Republic IV.441e)."These two parts... will exercise authority over the appetitive part which is the largest part and is insatiable for possessions. They will watch over it to see that it is not filled with so-called pleasures of the body, and by becoming enlarged and strong thereby no longer does its own job but attempts to enslave and rule over those over whom it is not fitted to rule, and so upsets everyone's whole life" (Republic IV.442a-b).

This organization of the three parts of the soul ("reason" (τὸ λογιστικὸν), "spirit" (τὸ θυμοειδές), and "appetite" (τὸ ἐπιθυμητικόν)) is justice in a human being.

"[Justice] does not lie in a man's external actions, but in the way he acts within himself.... He does not allow each part of himself to perform the work of another, or the parts of his soul (τὰ ἐν τῇ ψυχῇ γένη) to meddle with one another. He regulates well what is really his own and rules himself. He puts himself in order, ... and harmonizes the three parts of himself... He thinks that the just and beautiful action, which he names as such, to be that which preserves this state (ἕξιν) and indeed helps achieve it, wisdom to be the knowledge which oversees this action; and believing and naming the unjust action to be that which ever tends to, an unjust action to be that which always destroys it, and ignorance the belief which oversees that" (Republic IV.443d-444a).

A solution is to a puzzle about "wisdom and truth and the best state of [the] soul"

Socrates, in the early dialogues, suggests that there is a certain competency involved in living the good life, that this competency is a state of the soul, and that the person who has the traditional virtues is the one who has this competency. The person who acts in terms of these virtues chooses wisely and thus arranges things in his life so that he is "happy" (εὐδαίμων).

Now, in the Republic, Socrates articulates this view about the virtues and happiness in terms of the parts of the soul. He explains that justice is the state of the soul that constitutes the competency, that justice in the soul is a matter of the three parts of the soul each doing its own job. In the just soul, the part with reason leads. It is not confused about what is good and what is bad. In this way, the person whose soul is just is wise because the part with reason exercises "forethought in behalf of the entire soul" and hence arranges things so that he is "happy" (εὐδαίμων). He is also courageous and brave because the spirited part of his soul holds to the declarations of reason against the desires of appetitive part, and he is temperate because the appetitive part is controlled.

  "Then, wouldn't these two parts also do the finest job of guarding the whole soul and the body (ἁπάσης τῆς ψυχῆς τε καὶ τοῦ σώματος) against external enemies--reason by planning, spirit by fighting, following its leader, and carrying out the leader's decision through its courage?
  Yes, Socrates, that is true.
  And it is because of the spirited part (τὸ θυμοειδὲς), I suppose, that we call a single individual courageous (ἀνδρεῖον), namely, when it preserves through pains and pleasures the declarations of reason about what is to be feared and what isn't.
  That is right.
  And we'll call him wise (σοφὸν) because of that small part of himself that rules in him and makes those declarations and has within it the knowledge (ἐπιστήμην) of what is advantageous for each part and for the whole soul, which is the community of all three parts.
  And isn't he temperate (σώφρονα) because of the friendly and harmonious relations between the same parts, namely when the ruler and the ruled believe in common that the rational part should rule and don't engage in civil war against it?
  Temperance is surely nothing other than that, both in the city and in the individual" (Republic IV.442b-d).

Perseus Digital Library:
Plato's, Republic

Henry George Liddell, Robert Scott, A Greek-English Lexicon:
ἁρμονία, harmonia, noun, "means of joining, fastening,"
ἐπιθυμητικός, epithymētikos, adjective, "desiring," (τὸ ἐπιθυμητικός = "the part (of the soul) with appetites),"
θυμοειδής, thymoeidēs, adjective, "high-spirit," (τὸ θυμοειδές = "the (part of the soul) with spirit"),
λογιστικός, logistikos, adjective, "skilled in calculating," (τὸ λογιστικόν = "the (part of the soul) with reason"),
οἰκεῖος, oikeios, adjective, "proper, fitting, suitable,"
προσήκοντα, prosēkonta, participle as adjective, "befitting, proper"