  The tempting line of argument that McDowell is concerned to resist starts by proposing that since hallucinations can be subjectively indistinguishible from genuine perceptions, the differences between your genuine perceptions and your hallucinations must be external to how things are with you subjectively. An epistemic claim is then made: Matters external to how things are with you subjectively cannot intelligibly contribute, even in part, to your epistemic standing on some question. For such matters will be beyond your ken, and matters beyond your ken cannot make any difference to your epistemic standing. The conclusion that is then drawn is that when you genuinely perceive the world your epistemic grounds for making world-directed perceptual judgements are the same as, an hence no better than, those available to you when you have a subjectively indistinguishible hallucination.