So, I am interested in illusion (and hallucination, and generally any error related to perceptual experience) because illusion (and hallucination) undermine the place perceptual experience has in showing us the actual world.
I hold that Illusions/hallucinations are cases in which one has a perceptual experience of something (there seems to be x) in which there is actually no such thing (there is no x). To reiterate, this complicates taking perceptual experience as a source of knowledge. It creates an epistemological problem — a problem of grounding or foundations. Given the possibility of an illusion of x: A perceptual experience might be of some x, and so I conclude there actually is that x; yet it might be an illusory experience, and so there is no actual x.
A perceptually experienced x may still be possible but that risks placing perceptual experience, I think, on the same level as thought. It risks giving us what is possible, not actual. If that is all it gives us, then: how can perceptual experience show us the actual world? And without it, how can we know what is in the actual world?
In such a case, at best, perceptual experience shows you what is possible and not actual — because, with illusion/hallucination, what appears to be the case is not actually the case (further, with ‘impossible objects‘ it might not even do that). If perceptual experience only shows us a possible world, I think it leaves us only with variations of what can be thought. My worry is that, in such a position, we are in as great a state of ignorance as if we had no experience at all.
Such issues suggest to me that, when thinking about the actual world, how one deals with claims about illusion/hallucination matters. It matters how one deals with claims about illusion in light of accounts about (a) the actual world and (b) how we know about the actual world. If one can eliminate them in one’s theory, this is an epistemological advantage for one’s theory.
How can one deal with claims about illusion? Here are four ways. (They may or may not correspond to moves by contemporary perceptual theories, e.g., disjunctivism, representationalism). An experience E is claimed to be illusory. So we:
(a) Accept illusion for the particular case of E, but not the general case: Some experience E is illusory; E does not show the actual world. E must be treated as only showing what is possible, rather than actual.
(b) Extend illusion to the general case of E, i.e., for all cases of experience: Some experience E is illusory; NO experience (including E) shows the actual world. ALL instances
of experience must be treated as only showing what is possible, rather than actual.
(c) Deny the particular case of E: Some experience E is claimed to be illusory; E is not illusory. E might show the actual world.
(d) Strongly deny the particular case of E: Some experience E is claimed to be illusory; E is not illusory. Experience E shows us the actual world.
‘c’ and ‘d’ deny that there is an illusion in the case of E. Then they assert to different strengths that experience shows the actual world. The difference in strength concerns the role one gives experience. ‘d’ is preferable if you think it should be used to pick out the actual world. That experience might pick out the world (‘c’) is less compelling than that experience does pick out the actual world (‘d’).
But how can one question the idea that E is illusory?
One does so by questioning either claims about the appearances or claims about reality. I take the latter approach with respect to reality in time.
Next (page 4 of 5 below): Why Time?