Catharine Trotter Cockburn challenges voluntarist views held by British moral philosophers during the first half of the eighteenth century. After introducing her metaphysics of morality, namely, her account of human nature, and her account of moral motivation, which for her is a matter concerning the practice of morality, I analyze her arguments against theological voluntarism. I examine, first, how Cockburn rejects the view that God can by an arbitrary act of will change what is good or evil; second, how she (...) challenges views that understand the initial creation of the world solely in terms of divine will and draws attention to the role that the divine understanding plays in God’s creation; and third, how she argues that moral obligation does not require a superior lawmaker. I conclude by highlighting how Cockburn’s arguments not only challenge voluntarist views, but also offer support for her moral fitness theory. (shrink)