  This version of the causal argument does not rely on the general principle ‘same proximate cause, same immediate effect’, so a proponent of the argument may allow that there is a kind of mental event that occurs when one perceives the world which doesn’t occur when one hallucinates. Moreover, a proponent of the argument may also allow that there is an explanatory role to be played by the kind of mental event that only occurs when one perceives the world, which cannot be performed by appealing to the kind of mental event that is common to perception and illusion, plus some further non-mental conditions. (For this idea see Peacocke 1993 and Williamson 2000).  However, the argument does put pressure on the disjunctivist to accept that there is a certain kind of mental event common to perception and hallucination—one that we should be able to give a positive, non-disjunctive account of. (See Burge 2005, 2010 and 2011 for arguments to the effect that a denial of this claim is empirically untenable and incompatible with the methodology of vision science.) It suggests that if one simply wants to claim that genuine perceptions are mental events of a kind that cannot occur when one hallucinates, one should not be concerned to argue for a disjunctive account of perceptual experience. One’s concern should simply be to oppose a conjunctive account of genuine perception. (For this line of criticism see Williamson 2000 and Johnston 2004).