The claim that all the virtues are somehow one is advanced in different ways by Socrates and Plato, by Plotinus and Augustine, and by Aquinas. The doctrine of the unity and the interconnection of the virtues is thus common to a number of major thinkers in both ancient and medieval philosophy. But it has hardly been a fashionable view in recent philosophy, and it is apt to seem paradoxical. The purpose of this essay is to indicate the structure of the doctrine as Augustine expounds it and to indicate its relevance to clarifying and making plausible certain other ethical doctrines in Augustine's thought.