This book covers questions 90-108 from Aquinas's Summa Theologiae. The selected questions examine the nature of human acts, virtues, and vices.  Aquinas argues that the moral quality of an action is determined by its object, end, and circumstances, with the ultimate goal being the attainment of happiness through union with God.  In this set of questions, Aquinas defines “virtue” and highlights the essential role virtues play in achieving moral excellence and true happiness.