 There is no doubt that (a) and (b) have considerable plausibility. Nonetheless, they are controversial. To explain the truth of (a) and (b), Dretske counted on his conclusive reasons analysis of perception. His critics may cite the safe indication account of perception as the basis for rejecting (a) and (b). Luper (2006), for example, argues against both, chiefly on the grounds that we can perceive and know some elusive claims (such as not-mule) indirectly, by directly perceiving claims (such as zeb) that entail them.