James E. Bruce explores the relationship between morality and God's free choices in the thought of Francis Turretin (1623-1687). The first book-length treatment of Turretin's natural law theory, Bruce provides an important theological backdrop to Early Modern moral and political philosophy. Turretin affirms Thomas Aquinas's approach to the natural law, calling it the common opinion of the Reformed orthodox, but he develops it, too, by introducing a threefold scheme of right (ius)-divine, natural, and positive-to explain how change within the law is possible. So, for example, God can change the specific day for Sabbath observance from Saturday to Sunday-from positive right-without changing the natural law precept that finite creatures ought to rest. Yet even with respect to the natural law God is still free: God's free choices determine the natural law insofar as the natural law is constituted by the nature of the things God has chosen to create. God cannot make a murderable man, but he can make a world in which there is no such thing as murder-but only by choosing to create a world that contains no such a thing as man.