Book 6, Chapters 1-2. Having discussed virtues of character, Aristotle turns to virtues of thought. As he did before discussing the other virtues, he reviews the components of the soul. Again, the soul has two parts: one rational, one nonrational. The rational part has scientific and rationally calculating—or deliberating—parts. The function of the rational part of the soul is truth; hence, the virtues of that part of the soul will be “the states that best direct it toward the truth.”
As before, the soul’s makeup and inner workings shape the practice of virtue. When dealing with virtues of character, Aristotle confined his discussion to the nonrational part of the soul; now, he examines the rational part, which in turn has both scientific and deliberating parts—which deal, respectively, with unchanging principles and things which admit of various possibilities.
Book 6, Chapters 3-6. Aristotle identifies five states in which the soul grasps the truth: scientific knowledge, craft knowledge, prudence, wisdom, and understanding. Both understanding and scientific knowledge are concerned with learnable principles that don’t change. Craft knowledge is a state oriented toward producing something. Prudence is the ability to “deliberate finely […] about what sorts of things promote living well in general.” Prudence is particularly about human concerns, “things open to deliberation.” These things include both universals and particulars.
Just as states are relevant to virtues of character, so there are states that produce virtues of thought. For Aristotle’s purposes, the most significant of these is prudence, which particularly has to do with deliberating about virtue.
Book 6, Chapters 7-13. Good deliberation, Aristotle explains, isn’t just any sort of rational calculation; after all, a base person can deliberate correctly, but arrive at the conclusion he wishes to reach (which is a base one); whereas good deliberation must accord with what’s beneficial. Prudence is important because virtue is a state in accord with correct reason, and prudence is correct reason in the area of virtue.
While anyone can engage in deliberation, only a virtuous person can deliberate well. That’s because good deliberation depends on the virtue of prudence, which draws upon reason rather than on base desires.