A patient and faithful working of primary Thomistic texts, this volume presents a systematic and unified character of Aquinas's theory of moral agency as it relates to human action. Focusing especially on the Summa theologiae, Ralph McInerny carefully argues that Aquinas's theory of moral action stands up to contemporary needs and remains adequate against contemporary criticism. This lively and incisive study by a first-rate scholar demonstrates a breadth of knowledge of Aquinas in a novel, yet scholarly, fashion.