  In response to this criticism, McDowell has said that in accepting his disjunctive account of experience we need not pretend to have an argument that can prove that we are not being deceived using premises we can affirm without begging the question against the sceptic. What the disjunctive account does achieve, though, is to show we can resist sceptical arguments that appeal to the “highest common factor” conception of experience—that conception of experience according to which genuine perceptions and subjectively indistinguishible hallucinations do not differ in their epistemological significance. For the disjunctive account of experience blocks the inference from subjective indistinguishability to the highest common factor conception. According to McDowell’s diagnosis, the move from subjective indistinguishability to the highest common factor conception depends upon an illegitimate view of self-knowledge. (For a similar proposal see Williamson 2000). And McDowell argues that this illegitimate view of self-knowledge itself makes unintelligible a characteristic of experience that the sceptical argument does not usually question—that our perceptual experience at least purports to reveal how things are in the objective world.