 For Aquinas the norms of morality are defined in terms of their relationship to human happiness. We have a natural inclination toward our good, which is happiness, and it is that good that determines the content of morality. So like Aristotle, Aquinas holds a eudaimonistic theory of ethics: the point of the moral life is happiness. That’s why Aquinas can understand the will as an intellectual appetite for happiness. All of our choosing is aimed at the human good (or at least, it’s aimed at the human good as we conceive it). And choices are good—and, indeed, fully intelligible—only when they are aimed at the ultimate end, which is happiness. So Aquinas just defines the will as the capacity to choose in accordance with a conception of the human good—in other words, as intellectual appetite.