Aquinas’ list of virtues does not altogether tally with Aristotle’s, though he works hard to Christianize some of the more pagan characters who figure in Ethics. Aristotle’s ideal man is great-souled, that is to say, he is a highly superior being who is very conscious of his own superiority to others. How can this be reconciled with the Christian virtue of humility? By a remarkable piece of intellectual legerdemain, Aquinas makes magnanimity not only compatible with humility but part of the very same virtue. There is a virtue, he says, that is the moderation of ambition, a virtue based on on a just appreciation of one’s own gifts and defects. Humility is the aspect that ensures that one’s ambitions are based on a just assessment of one’s defects, magnanimity is the aspect that ensures that they are based on a just assessment of one’s gifts.
Anthony Kenny, Medieval Philosophy, Vol 2., 73.