The Human Function and Aristotle's Art of Rhetoric
“The current attempts to derive ought from is, based on the recent popularity of “virtue theory,” construct inferences from practices, broadly conceived and empirically observed, through the skills and abilities required to engage in those practices, to a set of activities worth pursuing for their own sake, to the virtues of character that make those activities possible, and therefore to the human ergon and the good for man. There must be something right about such inferences[…]But there also is something wrong with these inferences: a purely empirical investigation of the range of human practices and skills will not be able to derive the human ergon from the properties of the good thief, the good bureaucrat, the good lawyer, and the good adulterer, nor from simple, non-normative generalizations based on them.[…]The argument in the first chapters of Aristotle’s Rhetoric can serve as a model for such derivations, highlighting their dangers and showing what it takes to get those arguments right.”
Garver, Eugene. "The Human Function and Aristotle's Art of Rhetoric." History of Philosophy Quarterly 6, no. 2 (April 1989): 133-145. http://www.jstor.org/stable/27743888.