 Similarly, in the case of perception—understood as a kind of non-demonstrative (i.e., defeasible, or non-monotonic) inference from sensory ‘premises’ to perceptual ‘conclusions’—the claim that perceptual systems are informationally encapsulated is equivalent to the claim that “the data that can bear on the confirmation of perceptual hypotheses includes, in the general case, considerably less than the organism may know” (Fodor, 1983, p. 69). The classic illustration of this property comes from the study of visual illusions, which tend to persist even after the viewer is explicitly informed about the character of the stimulus. In the Müller-Lyer illusion, for example, the two lines continue to look as if they were of unequal length even after one has convinced oneself otherwise, e.g., by measuring them with a ruler (see Figure 1, below). 