Aquinas on the function of moral virtue

Aquinas is quite clear about the definition of moral virtue and its eff ects, but he devotes little space to its function: How does it accomplish what it accomplishes? Aquinas's treatment of the acquired moral virtues in our non-rational appetites reveals that they have at least two functions: they make the soul's powers good instruments of reason, and they also calm the appetites so that one can make moral judgments with an unclouded mind. Virtue in the will has a diff erent, "strong directive" function: it directs our will to certain goods prior to reason's forming its judgment. Aquinas must also hold that the virtues of the non-rational appetites exercise strong direction as well, but we cannot see why unless we examine his account of the infused moral virtues.