 A third problem with the statistical approach concerns whether it can shed any light on the specific issue of ontological parsimony. At first glance, one might think that the postulation of extra entities can be attacked on probabilistic grounds. For example, quantum mechanics together with the postulation ‘There exist unicorns’ is less probable than quantum mechanics alone, since the former logically entails the latter. However, as Sober has pointed out, it is important here to distinguish between agnostic Occam’s Razor and atheistic Occam’s Razor. Atheistic OR directs theorists to claim that unicorns do not exist, in the absence of any compelling evidence in their favor. And there is no relation of logical entailment between \(\{QM +\) there exist unicorns\(\}\) and \(\{QM +\) there do not exist unicorns\(\}\). This also links back to the terminological issue. Models involving circular orbits are more parsimonious—in the statisticians’ sense of ‘parsimonious’—than models involving elliptical orbits, but the latter models do not postulate the existence of any more things in the world.