Book IV ends the conversation “pertaining to the gods” between Socrates and Glaucon. It begins with an interruption by Adeimantus, who has thus far been remote from the conversation. His accusation against Socrates is that the men will lead unhappy lives. The communistic life, as described at the end of Book III, does not allow for the blessed joys in life.
Socrates makes his apology defending the total communism assigned to the guardians, on the grounds that the group in the Piraeus initially began this inquiry by looking to the happiness of the whole city, not merely the happiness of one particular group within the city. This was in order to find justice in the best governed city, and injustice in the worst governed city. However, now Socrates announces a new beginning. Now, they examine each group in the city according to their happiness so the city will be better apportioned toward justice, for the guardians will not successfully complete their job unless they are found to be happy, according to their share of nature’s happiness, as described by the pedestrian, Adeimantus. It is noted that each person’s education and rearing will allow the regime, once well-founded, to “roll on like a circle in its growth” (424a) -this is the purpose of their education: to create an enduring regime, i.e. one that will last through the changes.
Socrates and Adeimantus take up the staff of the lawgiver, as Socrates the need for the charming lawgivers who set the standard for the future men of the law, always creating contracts and trying to limit the wrongdoings of others, not realizing they are cutting off the heads of a hydra. The first laws are born, and interpreted, by the gods. These lawswill come from the ancestral god.
Glaucon interrupts and redirects the conversation away from the failings of his brother. If the city is correctly founded, then it will be perfectly good, and therefore it will be wise, courageous, moderate and just (427e). These four categories will later come to comprise the four Cardinal Virtues, according Thomistic theology. The terms crdinal comes from the Latin word cardo, meaning “hinge”. A good life “hinges” upon these four virtues. At any rate, Glaucon and Socrates look to find Wisdom, courage, and moderation. In the city, wisdom is found in the ruling part, the guardians. Courage is found to be a kind of preservation and power of the noble education and to have a lawful opinion about what is terrible and what is not, like those who dye wool with a foundational color so that none of the other colors can wash it away -it is steadfast in its right and lawful opinion. Socrates calls this eidos “political courage (429c). Moderation is a kind of harmony and mastery over oneself, taming one’s impulses, it implies: that which is better by nature is master over that which is worse.
Finally, Socrates and Glaucon agree to proceed like hunters to capture sight of justice in the city, though it will be hard and steeped in shadows. Suddenly Socrates catches sight of justice -it comes to light as the practice of minding one’s own business, when it comes into being in a certain. Justice provides the power by which the other virtues may come into being, and once it has come into being it provides the other virtues with preservation as long as it’s in the city. Note, this definition is mostly closely akin to Cephalus’s famous notion of justice, only without the piety ascribed to his definition.
In continuing with the parallel between the city and man, Socrates now considers justice within one man. Like the city, it is the cause of each part of the soul working in harmony and fulfilling their function, i.e. minding their own busines, and they are ruled by the calculating part, the wisdom. The three parts of the soul, or castes in the city, do not meddle with one another, and instead each part minds his own internal business, and he sets his house in good internal order and becomes entirely “one from many”, moderate, and harmonized. Thus, Socrates and Glaucon have found the just man and the just city. Unlike other dialogues, the conclusion is not met aporeia, but rather the politeia has an answer. It is a dogmatic dialogue, which leads us to question the integrity of Socrates. Is he giving a true account of the nature of justice? Or is he simply trying to charm the others? At any rate, what remains to be considered in the dialogue is whether it is profitable and preferable act justly or unjustly a la Gyges.