Aristotle on Justice
Considering whether The Philosopher agrees or disagrees with Plato.
First, a non-sequitur to the content of Book V of Nicomachean Ethics: Aristotle is an exhausting writer. His sentences are byzantine, his obsession with homonymy is frustrating, and, though his ultimate conclusions are well reasoned, monotonously articulated.
Points to Plato for style.
Though he does not develop this whatsoever, I think it's interesting that Aristotle distinguishes between the good man and good citizen. He does so explicitly: "being a good man is not the same as being every sort of good citizen" (1130b28-29). Rightly so, considering he has admitted that "the unfair is not the same as the lawless" (1130b11-12) and, later on, "what is legally just is different from what is primarily just" (1136b37).
A question I have is to what extent Aristotle's conception of the soul and, therefore, justice, is aligned with Plato's. For example, Aristotle (like Thrasymachus) regards "justice [as] the only virtue that seems to be another person's good, because it is related to another; for it does what benefits another" (1130a4-6). Later, Thrasymachus is echoed again when Aristotle describes "justice [as] the intermediate between doing injustice and suffering injustice" (1133b31-32).
Yet, he goes on to describe how one can be just and unjust to oneself insofar as he acknowledges that "in these parts [of one's soul] it is possible to suffer something against one's own desires [that is, the desires of the rational/human/divine part of the soul]. . . it is possible for those parts to be just to each other, as it is for ruler and ruled" (1138b6-9). Particularly in the italicized portion of the excerpt, Aristotle seems to buy into Plato's metaphysics of the human soul and what justice means therein.
More evidence abounds for Aristotle's agreement with Plato's conception of Justice and the soul in that he recognizes a spirited element of the soul that can cause someone to "inflic[t] these harms and commi[t] these errors, he does injustice and these are acts of injustice; but he is not thereby unjust or wicked, since it is not vice that causes him to inflict the harm" (1135b22-24).
Finally, even more evidence of Aristotle's agreement with Plato is his conception of justice as "the sort of proportion that mathematicians call geometrical" (1131b13), i.e., justice consists of equality between equals: "whenever equals receive unequal shares, or unequals equal shares, in a distribution, that is the source of quarrels and accusations", i.e., discord, chaos, disharmony: injustice (1131a23-24).