Augustine, from whose words this definition is gathered, and principally in De Libero Arbitrio.1 I answer that, This definition comprises perfectly the whole notion of virtue. For the perfect notion of anything is gathered from all its causes. Now the above definition comprises all the causes of virtue. For the formal cause of virtue, as of everything, is gathered from its genus and difference, when it is defined as a good quality; for quality is the genus of virtue, and the difference, good. But