 Euler’s rejection of the vis inertiae was not his only major reaction to Newton’s science. The question of whether to accept, and of how to interpret, absolute space, time and motion, and the related question of how to conceive of the relation between Newton’s work in natural philosophy and the flourishing Leibnizian-Wolffian metaphysics on the Continent, continued to drive conversations in the middle of the eighteenth century. Just a few years after Châtelet published her Institutions, Euler presented a novel approach to these two questions in a short paper entitled “Reflexions sur l’Espace et le Temps”, first published in 1748 in the Mémoires de l’Académie des Sciences de Berlin. The Berlin Academy had been witnessing a vociferous debate between Wolffians and Newtonians since 1740 (a debate that would continue until roughly 1759), one in which Euler played a role. Whereas one might regard the British philosophers, especially Berkeley and Hume, as arguing that philosophical principles and commitments take a kind of precedence in driving one’s interpretations of the concepts of force, motion, space and time, Euler argued that natural philosophy—specifically, mechanics—ought to take precedence. The famous first sentence of his essay indicates why: he contends that the principles of mechanics—for instance, the principle of inertia—are so well established that it would be foolish to doubt them (Euler 1748: 324). In particular, if one’s metaphysical commitments stand in tension with the concepts of space and motion found in geometry and mechanics, then one must adjust those commitments accordingly. Euler then presented a clever argument: the law of inertia picks out rectilinear motion as a special kind of motion, so to apply it to bodies in nature, there must be a clear meaning to the idea of a straight line. But if space is merely the order of relations amongst material bodies, then any set of reference bodies we use to determine which motion is straight could itself be in motion. So to employ the idea of rectilinear motion, we require the notion of absolute space (see DiSalle 2006, 36-37).