This book deals with a neglected episode in the history of logic and theories of cognition: the way in which conceptions of inference changed during the seventeenth century. The author focuses on the work of Descartes, contrasting his construal of inference as an instantaneous grasp in accord with the natural light of reason, with the Aristotelian view of inference as a discursive process. Gaukroger offers a new interpretation of Descartes`s contribution to the question, revealing it to be a significant advance over humanist and late Scholastic conceptions. He argues that Descartes's account played a pivotal role in the development of our understanding of the nature of inference.