It is commonly assumed that the ergon argument consists in an inference which starts from the powers specific or peculiar to man and arrives at a definition of the human good. This would commit Aristotle to some form of naturalism which is either fallacious or at least not available to us because we cannot share his views about human nature. The purpose of the present paper is to show that this interpretation is unsatisfactory. Aristotle's argument is based on a general principle which may be reformulated as follows: "For any x, if x has an ergon y_, then x will be a good x, if and only if x produces good instances of y.rr The prior identification of the human ergon is then required in order to know what to evaluate when passing judgement on whether a human being is a good human being or not. The specification of the ergon must be achieved in an evaluatively neutral way since the ergon by itself does not provide any standard. I argue that this is conveyed by the expression energeia kai praxeis meta logou. Specifically human are all actions, right or wrong, which may be so precisely because they are accompanied by a logos. This in turn allows us to understand another troublesome expression Aristotle uses to refer to the characteristic activity of human beings: energeia kata logon e me aneu logou, "activity according to reason or not without reason." I argue that it is wrong to take the first disjunct as referring to the part of the soul which has reason in itself and the second one to the part of the soul which obeys reason (Irwin). The disjunction stands for positive and negative evaluation of human activity, respectively. To act well in the moral, practical and theoretical domain amounts to acting according to the logos, i.e. according to the corresponding virtues. Failure in the moral, practical and theoretical domain, on the other hand, is not totally irrational : the coward throws away his shield to preserve his life, a fool deliberates well towards a bad end, and a mistake in theoretical thought implies entertaining a logos which happens to be false. No inference from the ergon to the good takes place. On the contrary, the normative weight in Aristotle's ethics is carried by his analyses of the virtues. They provide the standards to judge good and bad performances of the human ergon. I finally argue that the conclusion of the ergon argument does not rest on metaphysical or psychological premises (although they are not inconsistent, of course, with the doctrine of potentiality and actuality, etc. in the Metaphysics nor with anything held in the De Anima). Accordingly, I fail to see here an attempt to "ground a universal answer to the question of how we should live in a theory of human nature."
Gomez-Lobo, Alfonso, "A New Look at the Ergon Argument in the Nicomachean Ethics" (1988). The Society for Ancient Greek Philosophy Newsletter. 158.