  We have seen that externalism is generally the denial of some internalist position, typically regarding accessibility or mentalism as accounts of justifiers. It is not surprising, then, that major arguments for externalism are, first, the failure or weakness in arguments for either accessibility internalism or for mentalism. Externalism fares best on this count in regard to accessibility internalism, since the arguments for that doctrine that we have considered are hardly compelling. Arguments for mentalism are in somewhat better shape, for in many contexts it does appear that a difference in mental states best explains a difference in the degree of justification for a belief. The support provided to mentalism by this explanatory argument is limited, mainly because explaining a difference in degree of justification falls short of establishing that it is plausible to hold that all justifiers are mental items. But it cannot be denied that the explanatory argument considered earlier goes some way in this direction.