 According to Snowdon (1980, 1990, 1998, 2011), the plausibility of this argument rests on a conception of perceptual experience that is wedded to a common element assumption—in particular, the assumption that the kind of experience one has when one genuinely perceives the world is one whose intrinsic nature is independent of the kinds of objects perceived. On this conception of experience, experiences are amongst the events, the intrinsic natures of which are independent of anything outside the subject. According to this view, the ‘looks’ sentences that are true in cases of hallucination and in genuine perception are made true by (or are true in virtue of) exactly the same kind of occurrence in both cases. Once this conception of perceptual experience is in play, we might then ask after the extra-mental conditions required for seeing objects in our environment. The Gricean thought experiments suggest that simply having an experience that matches your surrounding environment will not, in itself, be sufficient for seeing objects in your environment. So the temptation then is to think that an appropriate causal connection between your experience and those objects is necessary for you to see them. The motivation for the CTP is therefore undermined, according to Snowdon, unless it can be shown that it is part of our concept of perception that the common element claim assumed in the argument is correct.