No one before Saint Thomas and probably no one after, says John Finnis in this essay, has reflected on the internal structure of deliberation and choice with the care that he did. Of course, Thomas of Aquinas had to see that the explicit answer by Aristotle (in the Nicomachean Ethics) to the skeptical doubts as to "ethical truth" was not enough. In this essay, John Finnis examines the central elements of the response by Aquinas to skeptical relativism —a response that resolves many of the ambiguities and fills in many of the blanks in Aristotle’s response. The elements of Aquinas’ reflection are presented through an analysis of how free choices are made and implemented. The internal structure of action revealed by Saint Thomas —says Finnis— does not come from introspection as many of his followers have believed, but rather from an analysis of the concepts that we use when making our own choices and describing our conduct and that of others. In Finnis’ words, one of the most original theoretical achievements of Aquinas is based precisely on his analysis of the interrelationship between reason and will, an analysis not understood by Hume’s followers, who deny that reasons can constitute basic motivations for action.