  An influential argument against disjunctivism is the causal argument, first proposed by Howard Robinson (see Robinson 1985 and 1994). The simplest version of the argument appeals to the following two claims: (i) It is theoretically possible, by activating some brain processes involved when a subject genuinely perceives the world, to cause a hallucination subjectively indistinguishible from that perception—a ‘causally matching’ hallucination. (ii) It is necessary to give the same account of the experiences involved in genuine perception and hallucination when they have the same neural causes. So we should accept that the kind of experience that occurs when a subject perceives the world is one the subject could be having if she were hallucinating.