 A second conceptual point to make regarding the Machian relationism of Barbour and collaborators pertains to its motivations. Barbour claims, as we have already seen above, that only spatial angles – and not spatial scales, or a temporal timescale, or absolute velocities or positions – are directly empirically observable. Thus, the thought goes that an empiricist of good standing should favour (say) shape dynamics over GTR, for the former theory, unlike the latter, renders only such ‘directly observable’ quantities meaningful; it does not commit to any absolute quantities which are not ‘directly observable’. There are, however, two central points at which this reasoning could be questioned. First: one could repudiate Barbour’s empiricist motivations. Second: one could deny that only angles are directly observable, or, indeed, that this structure is directly observable at all (see Pooley 2013, p. 47). As Pooley points out, these are not the strongest grounds on which to motivate Barbour’s project. Rather, a better motivation is this: best-matched theories have the merit of ontological parsimony, as compared with the theories such as Newtonian particle mechanics or general relativity, to which the best-matching procedure is applied. A second motivation has to do with the potential of this research programme to present new avenues for exploration in the quest for a quantum theory of gravity.