The difference between Pierre Gassendi's (1592-1655) and René Descartes' (1596-1650) versions of the mechanical philosophy directly reflected the differences in their theological presuppositions. Gassendi described a world utterly contingent on divine will and expressed his conviction that empirical methods are the only way to acquire knowledge about the natural world. Descartes, on the contrary, described a world in which God had embedded necessary relations, some of which enable us to have a priori knowledge of substantial parts of the natural world. In this book, Professor Osler explores theological conceptions of contingency and necessity in the world and how these ideas influenced the development of the mechanical philosophy in the seventeenth century. She examines the transformation of medieval ideas about God's relationship to the Creation into seventeenth-century ideas about matter and method as embodied in early articulations of the mechanical philosophy. Refracted through the prism of the mechanical philosophy, these theological conceptualizations of contingency and necessity in the world were mirrored in different styles of science that emerged in the second half of the seventeenth century. – Table of contents : – Part I. Theology and the Philosophy of Nature: 1. Divine power and divine will in the Middle Ages: historical and conceptual background; 2. Baptizing epicurean philosophy: Gassendi on divine will and the philosophy of nature; 3. Providence and human freedom in Christian epicureanism: Gassendi on fate, fortune and divination; 4. Theology, metaphysics, and epistemology: Gassendi's 'Science of Appearances'; 5. Eternal truths and the laws of nature. – Part II. The Theological Foundations of Descartes' Philosophy of Nature: 6. Gassendi and Descartes in conflict; 7. Introduction: theories of matter and their epistemological connections; 8. Gassendi's atomism, an 'empirical' theory of matter; 9. Mathematizing nature: Descartes' geometrical theory of matter; 10. Conclusion: theology transformed and the emergence of styles of science.