 Plato’s method involves the provocative idea that justice in the city (polis) is the same thing as justice in the individual, just “writ large.” There are good reasons to worry about that assumption (Williams 1973; Keyt 2006). But in Plato’s sociology of the city, there are three classes engaged in a kind of division of labor. There is a guardian class which rules, a class of “auxiliaries” that provide the force behind the ruling, and the class of merchants that produce to satisfy the needs and desires of the city. Similarly, the psyche of the individual has three parts: a reasoning part to rule, a “spirited” part to support the rule of reason, and an appetitive part. Plato finds justice in the city to consist in each part “having and doing its own,” and since the smaller is just like the larger, justice in the individual consists in each part of the psyche doing its own work. (This grounds the idea, later enshrined by Justinian, that justice is “giving every man his due;” Justinian I.i). Further, Plato argues, justice is a master virtue in a sense, because in both the city and the psyche, if each part is doing its own job, both city and psyche will also have wisdom, courage, and moderation or self-discipline. This conception of justice sustains the contrast with the conventionalist view advocated by the Sophists. On the other hand, at least initially it leaves it an open question whether the just individual refrains from such socially proscribed actions as lying, killing, and stealing. Plato eventually seeks to show that someone with a healthy, harmonious soul wouldn’t lie, kill, or steal, but it is not clear that argument succeeds, nor, if it does, that that is the right understanding of why we ought not to lie, kill, or steal (Sachs 1963; LeBar 2013, ch. XII).