  This adumbrated version of empiricism is not without difficulties, as Gassendi is first to recognize. For one, having extended the warrant for the directly sensed to the indirectly sensed, we must find a way to confidently adduce evidence on behalf of what appears before the senses in indirect fashion only. For another, the supposition that solving for empirical knowledge presents a solution for all knowledge introduces the challenge of accounting for at least two apparent counterintuitive instances—knowledge of abstracta and knowledge of God and the cosmos (Gassendi subsumes the former to empirical knowledge on proto-Millian grounds, but exempts most theological and cosmological truth from empirical grasp (O II 398-424, 440-42)). Finally, he calls our attention to the recursive nature of empiricist doubts. If a lack of adequate sensory data strips away warrant for knowledge of the world then an empiricist theory of knowledge must also appeal to what the senses tell us, about what we can know of the world. The challenge, then, is to fashion an empirically adequate theory of acquiring sensory data. In formulating such an account, he anticipates crucial elements of later reliabilist theories of warrant.