Aristotle on Needs, Justice, and Exchange

In Nicomachean Ethics v 5, Aristotle holds that the measure of a just exchange is need (χρεία), since need serves as the motive for exchange. This article attempts to make sense of that puzzling inference from motive to measure. The solution is to appreciate the political dimension of Aristotle’s treatment of exchange: equal need-meeting is just because it keeps the polis together and, in that way, promotes the common benefit.