 But the priority monist can point to some crucial differences between gunk and junk that arguably justify only recognizing the metaphysical possibility of the former. Indeed it is doubtful that junk passes any of the tests for possibility that gunk passes. As to conceivability, it is hard to conceive that there is no limit to summation at which one has taken in everything. As to logical consistency, as least if this is judged with respect to classical mereology (arguably our best systematization of the logic of part-whole relations, and certainly the most orthodox), there is a difference as well: classical mereology has gunky models but not junky models. The onus is on the defender of junk to produce an overall logic of part-whole relations which tolerates junky models while being as plausible as orthodox classical  mereology.[48]  And as to scientific seriousness, while there is lots of work on physical cosmology, it appears that virtually all of it takes for granted that there is such a thing as the cosmos. Indeed it hardly seems to be an empirical question whether there could be such a thing as “the world,” and the reasons mentioned in §2.2 for thinking that there is such a thing equally serve as arguments against the prospect of there being only worldless junk.