Self-knowledge, externalism and scepticism, II - Scepticisms: Descartes and Hume

[FIRST PARAGRAPHS]The role of Professor McLaughlin's sceptic is to introduce certain 'sceptical hypotheses', hypotheses which imply the falsity of most of what we believe about the world. Professor McLaughlin asks whether these hypotheses are coherent and thus whether they can tell us anything about what are entitled to believe, or to claim to know. He concludes that, semantic externalism notwithstanding, these hypotheses are both coherent and threatening. I shall not question this conclusion but I do wonder whether the fate of scepticism hangs entirely on the coherence of the sceptical hypotheses.

I shall maintain that the root of scepticism, at least as we find it in Descartes and Hume, is the demand for certainty. Recent writers are likely to dismiss this demand for certainty: in their view, inconclusive evidence is quite sufficient both to justify belief and to give us knowledge (should the proposition in question turn out to be true). Like Professor McLaughlin, recent debate focuses rather on the possibility that we might have no evidence at all for our beliefs, that our belief-forming processes might be completely unreliable, undermining both knowledge and justification. It is the sceptical hypotheses which generate this worry - ordinary error does not - and so it is they alone, not the prosaic fact of our fallibility, which provide grounds for a real sceptical doubt.

Descartes and Hume are standard reference points for discussion of the sceptical hypotheses. Yet, I shall argue, in both Descartes and Hume, the sceptical hypotheses are secondary; what is really doing the work is their demand for certainty.

Furthermore Descartes, at least, suggests a way in which this demand might be motivated. Both philosophers do indeed raise 'the problem of the external world' but this is only one aspect of their scepticism; we can't dispatch either the Cartesian or the Humean sceptic just by demonstrating that thought or experience presupposes the existence of an external world. Their sceptical problem is more than the problem posed by the sceptical hypotheses.