 The link between the causal account of motion and the more general conceptual account of “true” motion was never obvious or straightforward. Descartes’s heliocentric causal account, in which the planets moved in vortices arising from the sun’s rotation, was disconnected from his abstract account of motion “according to the truth of the matter,” or “in the proper sense” (Descartes 1642, part II section XXV). Since there are innumerable objects to which one might refer the motion of any given body, the reference may appear to be a matter of arbitrary choice. The unambiguous reference for the motion of any body, he argued, is provided by the bodies immediately touching it. Newton, in response, argued that Descartes’s philosophical account of motion is flatly incompatible with his causal account. To Newton, it was incoherent to appeal to a causal account of motion when explaining the centrifugal tendency of a body in its orbit around the sun, while identifying its “proper” motion only by its relations to the bodies immediately contiguous to it (Newton 1684a, Stein 1967, Rynasiewicz 2014). Hence Newton’s argument that the only unambiguous standard of motion is a body’s change of position with respect to space itself. To space understood in this sense, as the universal frame of reference with respect to which the displacements of bodies constitute their true motions, Newton gave the name “absolute space” (1687b, p. 5ff). 