 Despite the influence of Newton’s “method” on eighteenth-century philosophy, it is obvious that the Principia’s greater impact on the eighteenth century is to have effected a branching within natural philosophy that led to the development of mathematical physics on the one hand, and philosophy on the other (Cohen and Smith, 2002, 1-4). And yet to achieve an understanding of how Newton himself approached natural philosophy, we must carefully bracket such historical developments—they did not solidify until sometime after 1750, a generation after Newton’s death. Indeed, if we resist the temptation to understand Newton as working within a well established discipline called mathematical physics, if we see him instead as a philosopher studying nature, his achievement is far more impressive, for instead of contributing to a well-founded field of physics, he had to begin a process that would eventually lead aspects of natural philosophy to be transformed into a new field of study. This transformation took many decades, involving a series of methodological and foundational debates about the proper means for obtaining knowledge about nature and its processes. Newton himself not only engaged in these debates from his very first publication in optics in 1672, but his work in both optics and in the Principia generated some of the most significant methodological discussions and controversies in the late seventeenth and early eighteenth centuries. These debates concerned such topics as the proper use of hypotheses, the nature of space and time, the best understanding of the forces of nature, and the appropriate rules for conducting research in natural philosophy. Newton’s achievement was in part to have vanquished both Cartesian and Leibnizian approaches to natural philosophy; in the later eighteenth century, and indeed much of the nineteenth, physics was a Newtonian enterprise more than anything. But this achievement, from Newton’s own perspective, involved an extensive, life-long series of philosophical debates. Those debates focused on numerous substantive issues, but also included extensive discussions of the proper methodology in natural philosophy.