 The virtues are a certain kind of psychological disposition (habitus): they are the perfections of those powers of the soul that are under our voluntary control. Aquinas devotes roughly a quarter of the Summa theologiae—mainly the 2a2ae—to his theory of the virtues, and also dedicates a series of disputed questions to the subject. He takes from Aristotle the familiar idea that it is through the repetition of certain kinds of actions that we acquire the virtues (as well, of course, as the vices): by acting honestly we acquire, over time, the virtue of honesty. Less familiarly, he imposes a very high standard on what counts as a virtue: it must be incapable of giving rise to an immoral act.