A virtue is a power of achieving and maintaining a state of excellence in the carrying out of a function. In the Republic, Plato makes large claims for the virtue of justice (dikaiosyne), calling it “a soul’s virtue” in carrying out its function of living well (See Rep. 353d-e). A soul (psyche) is that which animates disparate parts into a organic whole. Since this concern for properly functioning wholes is always in the backdrop of Plato’s notion of justice, it helps to know the end states that Plato has in mind for justice to accomplish and to overcome:
Stasis is a state of discord between parts that disrupt the healthy functioning of the whole. In Greek medicine it is almost a synonym for nosos, or disease. The contemporary medical term metastasis, which means the transfer of disease from one place in the body to another, has this original sense of stasis as its root. In its political meaning, stasis is a civil war, in which allegiance to party (and opposition to other parties) overcomes a common allegiance to a larger whole. Stasis is thus a broad term that implies internal divisions of all kinds of the parts within an encompassing whole.
Homonoia is the healthy condition from which stasis is the deprivation. Homonoia is defined by Liddell and Scott variously as “oneness of mind, unanimity, concord.” In the passage I will quote below, Grube and Reeve translate it as “a sense of common purpose.” It is derived from Greek prefix homo-, which means “alike” or “same” and nous which mean “mind” or “understanding” or “insight.” So homonoia is something like a common understanding or shared insight into the nature of a matter. Between the two poles of stasis and homonoia there exists an entire of spectrum of intermediate possibilities.
So the work of justice will be to purify its patient from notions of the good that are inherently factional and replace those with notions that are consistent with a larger homonoia. Consider the following conversation between Socrates and Thrasymachus from Book I of the Republic as an example:
Injustice, Thrasymachus, causes civil war [stasis], hatred and fighting among themselves, while justice brings friendship and a sense of common purpose [homonoia]. Isn’t that so?
Let it be so, in order not to disagree with you.
You’re still doing well on that front. So tell me this: If the effect of injustice is to produce hatred wherever it occurs, then, whenever it arises, whether among free men or slaves, won’t it cause them to hate one another engage in civil war [stasis], and prevent them from achieving a sense of common purpose [homonoia]?
What if it arises between two people? Won’t they be at odds, hate each other, and be enemies to one another and to just people?
Does injustice lose its power to cause dissension when it arises within a single individual, or will it preserve it intact?
Let it preserve it intact.
Apparently, then, injustice has the power, first, to make whatever it arises in — whether in a city, a family, an army, or anything else — incapable of achieving anything as a unit, because of the civil wars [stasiazonta] and differences it creates, and, second, it makes that unit an enemy to itself and to what is in every way its opposite, namely, justice. Isn’t that so?
And even in a single individual, it has by its nature the very same effect. First, it makes him incapable of achieving anything, because he is in a state of civil war [stasis] and not of one mind [homonoia]; second, it makes him his own enemy, as well as the enemy of just people. Hasn’t it that effect?
— Republic 351d-352a (Grube/Reeve translation)
Platonic justice (1) induces a respect for differences of function among the members of a whole, and (2) must presume a common allegiance toward that whole among these diverse parts. This common allegiance rests on the condition known as homonoia. In fact if we examine the Book 4 definitions of the four virtues, we can see how each has its place within a larger aim of achieving wholeness of a kind:
1. Justice — “Minding one’s own business and not being a busybody.” (433a) Comment — This is a call not to turn into factional antagonists against other functions within the city.
2. Courage — “Power and preservation, through everything, of the right and lawful opinion about what is terrible and what is not.” (430b) Comment — What is most terrible will turn out to be stasis: “Is there any greater evil we can mention for a city than that which tears it apart and makes it many instead of one?” (462a)
3. Moderation — “Unanimity (homonoia)…an accord of worse and better, according to nature, as to which must rule in the city and in each one.” (432a)
4. Wisdom — “A kind of knowledge belonging to some of the citizens that counsels not about the affairs connected with some particular thing in the city, but about how the city as a whole would best deal with itself and the other cities.” (428c-d)
So the concepts of stasis and homonoia are at the very heart of Plato’s Republic.