The Unintelligibility of Massive Error

1. Global scepticism and its refutation In The Significance of Philosophical Scepticism, Barry Stroud considers a haunting question: " Could not the external world be completely different from what we perceive it and believe it to be? " (Stroud, 1986: 210). Even the least persuasive sceptical arguments can evoke this doubt. For example, although the conclusion that our perceptual beliefs are in general untrust-worthy certainly doesn't follow, directly at least, from the fact that our senses sometimes lead us astray, reflecting on instances of illusion and perceptual error can engender the arresting thought that we might be experiencing systematic and general error or illusion. From this thought — the thought that our empirical knowledge-claims might generally be false or at least insufficiently justified — sceptical arguments are not far behind. To give one prominent argument: if knowledge is closed under known deduction , then, if we have empirical knowledge, we must know that we aren't in massive error; since global scepticism is false if we have any empirical knowledge, the closure principle entails that we can have empirical knowledge only if we know that the global sceptical possibility does not obtain. The trouble, of course, is that it is unclear how we could know this about the global sceptical possibility, especially, as seems reasonable, if appealing to putative instances of empirical knowledge is ruled out as question-begging. The closure argument tells against the policy of simply refusing to take seriously global sceptical doubts. But how might such doubts be dealt with? First note that, by itself, the sceptical possibility has no obvious direct epis-temic force: drawing sceptical conclusions requires something else, viz. an argument to parlay the doubts into conclusions about the difficulty of justifying empirical beliefs. Consequently, one way of refuting global scepti-26 Andrew Carpenter cism would be to block this move. In the light of the number of arguments advanced for global scepticism, however, this project quickly attains Her-culean proportions. Another tactic would be to engage the sceptical doubt itself, by arguing against the intelligibility of the very thought that the external world could be completely different from how we believe it to be. Since all versions of global scepticism arise from this thought, an argument holding that such massive error is incoherent or unintelligible would show that all arguments for global scepticism must be unsound. Note also that if the original sceptical question is unintelligible, then it …