  The naturalist-platonist response is two-pronged (Burgess and Rosen 1997, 2005; for criticism, see Linnebo 2006, Chihara 2006). The first prong is that no simple criterion for knowledge (or reliable belief or justified belief) has ever been devised that succeeds in ruling out knowledge of the abstract without thereby ruling out types of knowledge most naturalists would accept (Steiner 1975). A couple of examples: (i) the condition that p is a cause of the belief that p is too strong, as it rules out knowledge of the future; (ii) as the naturalist-platonist sees it, that abstract mathematical reality is thus-and-so is in fact part of the best explanation for the belief that p; hence an explanatory condition of this kind turns out to be compatible with platonism. Moreover, naturalist-platonists complain that even if a criterion were found that draws the line where the nominalist wishes it to be drawn, it would beg the question against platonism.