Often translated as "practical wisdom," the Greek word phronêsis derives from the verb phronein, meaning "to have understanding," or "to be wise or prudent." In its earliest uses the word is normative only in the sense that it signifies a correct cognitive grasp of some kind; only gradually does it come to be used in ethical contexts for a correct grasp of what ought to be done. For Plato and the other Socratics, phronêsis represents that aspect of our rational faculty that derives genuine knowledge about values and norms, that is, about the virtues (see especially Protagoras, Gorgias). The famous debate between the Socratics and their critics, such as the orator Isocrates, turned on the possibility of demonstrative knowledge in the sphere of virtue. Plato had attacked oratory on the grounds that its aim is not to discover what is morally right, but merely to persuade, and he offered in its place the Socratic method of dialectic, a cooperative search for the truth by means of hypothesis formation, critical examination and refutation, and hypothesis modification. Isocrates had characterized Socratic dialectic as mere eristic (Against the Sophists 1; Antidosis 261) or argument for argument's sake—probably for this reason, Plato is especially careful to distinguish the Socratic method from mere eristic in his Euthydemus—and referred to the Socratics as "disputers." But Plato devotes much argument to showing how the careful examination of various conceptions of the virtues can lead inexorably to a recovery of their essential nature, which resides in the soul of every person from birth.
Aristotle's treatment of phronêsis (Nicomachean Ethics VI.5 1140a24–b30; cf. 1141b8–1143a5) is similar in many respects to Plato's, but in his account the knowledge that we obtain of virtue is not the equivalent of scientific (demonstrative) knowledge (episteme): unlike episteme, which is concerned with necessary truths, phronêsis is always concerned with contingent truths. Aristotle defines phronêsis by reference to something more concrete and familiar, namely, the practically wise person, ho phronimos, someone who has phronêsis. It is the mark of the practically wise person, he says, to be able to deliberate well about what is good and advantageous for himself not merely in one area, such as health or strength, but as a means to human flourishing in general. The operation of phronêsis in Aristotle's account of the rational faculties appears to hinge on the application of general rules for right conduct (the orthos logos) to the particular circumstances of a given situation so as to result in action that will generally tend toward human flourishing. The phronimos is the person whose life is characterized by such applications of phronêsis and who, as a result, tends to flourish throughout his life. Such a person is said to be eudaimôn or "happy."
In contrast, the Stoics characterize phronêsis as a kind of scientific knowledge (episteme), namely, of what should be done or not. Although they differ amongst themselves about the precise relationship, the Stoics regard the other virtues as this sort of knowledge in more specific domains: justice concerns what should be done or not with regard to deserts, courage with regard to what should be endured, and moderation with regard to what should be chosen or avoided. But given the Stoics' conception of a good life as one lived in agreement with nature, knowledge of what should be done will depend on knowledge of both human nature and nature as a whole, and above all our role within the latter. Phronêsis, therefore, has a considerably larger scope for the Stoics than for Aristotle, and is possessed only by the Stoic ideal of the wise person.
For Epicurus, phronêsis has more to do with prudential reasoning. It is what enables us to assess the consequences of every choice and so calculate its overall value. It is thus crucial for leading a happy life—in fact, Epicurus regards it as even more precious than philosophy itself. In particular, he believes, it reveals that virtue and pleasure are inseparable: It is impossible to live pleasantly without living virtuously or, for that matter, to live virtuously without living pleasantly.
