St. Thomas Aquinas 
Treatise on the Virtues [PDF ebook] 

In his Treatise on the Virtues, Aquinas discusses the character and function of habit; the essence, subject, cause, and meaning of virtue; and the separate intellectual, moral, cardinal, and theological virtues. His work constitutes one of the most thorough and incisive accounts of virtue in the history of Christian philosophy. John Oesterle’s accurate and elegant translation makes this enduring work readily accessible to the modern reader.