Fred asked:

Does the argument from illusion show that there are no differences between the visual experiences involved in veridical perception, illusion, and hallucination?

Answer by Helier Robinson

Yes, Fred, definitely. That is the difficulty with the argument: it has never been refuted, but its conclusion is almost universally rejected, irrationally. The conclusion is that all visual (indeed, perceptual) experiences are representations of reality, not reality itself. That is, the only explanation of illusions is that they are misrepresentation of reality, not reality itself, because they are contradictions between the senses, or contradictions between perceptions and well-established beliefs; and there are no intrinsic differences between veridical and non-veridical perceptions, in which case all perceptions are representations. This means that empirical objects around us — indeed, the entire empirical world — is a representation of the real world, not itself the real world.

This leads to the question: what is the real world like? There are two answers, ultimately the same: the philosophic answer is that it is metaphysical, the scientific answer is that it is theoretical. You can begin to get a handle on all of this if you ask about the nature of your own body: is it real, or only an image of your metaphysical/ theoretical body?