 That is, relationists can allow ‘true’ motions if they offer an analysis of them in terms of the relations between bodies. Given this logical point, we are led to the second question: (ii) is true motion definable in terms of relations or not? (And if one hopes to give an affirmative answer, what kinds of relations are acceptable to use in the reductive definition?) It seems reasonable to call this the issue of whether motion is absolute or relative. Descartes and Mach were relationists about motion in this sense, while Newton was an absolutist. In the case of Einstein and GTR we linked relational motion to the satisfaction of Mach’s Principle, just as Einstein did in the early years of the theory. Despite some promising features displayed by GTR, and certain of its models, we saw that Mach’s Principle is certainly not fully satisfied in GTR as a whole. We also noted that in the absence of absolute simultaneity, it becomes an open question what relations are to be permitted in the definition (or supervience base) – spacetime interval relations? Instantaneous spatial distances and velocities on a 3-d hypersurface? The shape dynamics program comes at this question from a new perspective, starting with momentary slices of space (with or without matter contents) which are given a strongly relational – as opposed to absolute – interpretation. However, we argued that it ultimately remains unclear whether this approach vindicates Mach’s Principle.