 (2) It has often been objected that philosophers who have made use of the argument from illusion that they neglect the fact of perceptual constancy. In his later works Broad admits that this complaint is justified. However, the “recognition of the phenomenon of constancy merely shifts the point of application of the argument” (1947b, p. 112). There is a class of perceptual experiences of a material object, X, where constancy holds; there is also a class of experiences of X where constancy breaks down. In theory it is logically possible to hold that the facing surface of X is sensuously presented in the perceptual experiences belonging to the first class but not in the experiences belonging to the second class. “But, in view of the continuity between the most normal and the most abnormal cases of seeing, such a doctrine would be utterly implausible and could be defended only by the most desperate special pleading” (1952a, p. 9).