Causation and perception: the puzzle unravelled
1. Attempts to give a philosophical analysis of perception haven't come very far since Grice's causal theory of perception (Grice 1961). According to the causal theory, S sees that o is F if and only if S has a visual experience as of o's being F; o is F; and o's experience depends, causally, on o's being F. The point of the causal-dependence clause is to rule out what came, later on, to be known as veridical hallucination, i.e. cases in which you enjoy a veridical visual experience which nevertheless falls short of being genuinely perceptual (Lewis 1980). Grice's example went like this: suppose there is a clock on the shelf and that you have a veridical experience as of its being there. But suppose that the cause of your experience is not the clock's being on the shelf, but, say, post-hypnotic suggestion. In such a case, you do not succeed in seeing that the clock is on the shelf, even though your experience is veridical. What explains this failure, so Grice proposed, is the fact that in this case the requirement of causal dependence is not met.