Nothing in Excess: The Ethics of Measure and the Mean in Plato and Aristotle

Aristotle's doctrine of the mean is one of a handful of ancient philosophical theories that is widely known among philosophers generally. By contrast, Plato's discussions of measure are hardly known even among ancient philosophy specialists. It is unsurprising, then, that the influence of those discussions on Aristotle's doctrine has hardly been acknowledged, let alone examined in detail. The project of this dissertation is to fill this gap in our understanding; it is to examine the relationship between Plato's measure and Aristotle's mean.

In order to undertake this examination, accurate accounts of Plato's measure and of Aristotle's mean are needed. With regard to Plato, I pay particular attention to the Statesman and the Philebus. Out of the entire Platonic corpus, the passage on the art of measurement from the Statesman (283c-285c) is the clearest source of inspiration for Aristotle's doctrine. The standard interpretation of this difficult passage, however, is fundamentally mistaken, and so an alternative interpretation is needed. The discussions of measure in the Philebus supplement and illuminate this passage from the Statesman by elucidating the philosophical roles played by measure: measure both gives particular things their identities and serves as the relevant norm compliance with which renders those things good.

Turning to Aristotle, I develop a novel account of the doctrine of the mean. The need for such an account is especially pressing inasmuch as Aristotle's doctrine is often interpreted in a way that renders the doctrine philosophically implausible but that also has very little textual support. The novel account offered in this thesis is shown to handle readily the most common objections to Aristotle's doctrine.

With accurate accounts of measure and the mean, I then turn to comparing them along four points: normativity, ethical knowledge, what compliance with measure or the mean consists in, and absolutism (as opposed to relativism). The differences between Aristotle and Plato with regard to these four points reveal, I conclude, a fundamental difference in approach to ethical philosophy. For Plato, ethical theorizing is to be undertaken for the sake of gaining greater theoretical understanding; for Aristotle, its benefit is primarily practical.