Chapter 4 - Losing grip on the world: from illusion to sense-data

Summary

The claim that perceptual illusions can motivate the existence of sense-data is both familiar and controversial. Admitting that various illusions do not give evidence for sense-data considerably limits the power of the argument from illusion and brings out its distinctness from the argument from perceptual relativity. To reach these conclusions, the chapter examines the role of ambiguity in perception, its connection to illusion, and the link reference to every element of this discourse. The inference from illusions to sense-data has been used to additionally argue for indirect realism, the claim that the immediate objects of perception are always (or at least typically) sense-data. The chapter is concerned with the extent to which a successful form of perceptual reference, what it calls acquaintance, is involved in perceptual awareness. Understanding why some illusions do and some do not support the existence of sense-data is a non-trivial task.