Abstract: Here is a familiar story. Up until the early 17^th century, physics was a part of philosophy. Then the Scientific Revolution happened – including Newton’s Principia of 1687 -- and after this physics was a separate discipline. This story has been told many times, and challenged in many ways, but a common thread persists in which we think of 18^th century physics as having already separated from philosophy, as broadly familiar from the perspective of contemporary physics, and as a stable period of normal science within the “Newtonian paradigm.” I will argue that this obscures the deep philosophical reasons that drove the separation of physics from philosophy and skews our understanding of the philosophical landscape in the 18^th century. At stake were two central issues from the period, material substance and causation, along with the appropriate methodologies for tackling them. The relevant arguments unfolded over the course of the 18^th century in the work of such figures as Leibniz, Malebranche, Wolff, Maupertuis, Du Châtelet, Euler, d’Alembert, Boscovich, Kant, and Laplace. It was only late in the 18^th century that the split took hold, with consequences that continue to play out in philosophy today. I will invite you to rethink how you think (and teach) about the 18^th century. (This talk is largely based on joint work with Marius Stan, including an earlier paper by the same title and our forthcoming book Philosophical Mechanics in the Age of Reason, OUP.)