Antoine Arnauld is well known as a passionate defender of Jansenism, specifically Jansen’s view on the relation between freedom and grace. Jansen and, early in his career Arnauld, advance compatibilist views of human freedom. The heart of their theories is that salvation depends on both the irresistible grace of God and the free acts of created things. Yet, in Arnauld’s mature writings, his position on freedom seems to undergo a significant shift. And, by 1689, his account of freedom no longer (...) seems Jansenist. In this paper, we offer an interpretation of Arnauld’s mature view on freedom, with a focus on his claim that freedom requires a “power to the opposite.” In order to see what he means by this, we look to several under-examined texts in his corpus for clues about how he understands the related topics of “infallible determination,” habit, and primo-primi motus. We argue that Arnauld’s mature view on freedom should be understood as libertarian. (shrink)