 The skeptics challenge strikes at the claim made by the Naiyāyikas that perception should be non-erroneous (avyabhichāri) and well-ascertained or free from doubt (vyavasāyātmaka). They ask: how do we distinguish between veridical perceptions and the non-veridical ones? In case of a perceptual doubt, say, seeing something at a distance which looks like a pole or an old tree-trunk, we are uncertain which it is but are a priori sure it cannot be both. In case of perceptual illusion, I see a snake but I misperceive as there is only a rope in front of me. Illusoriness of the experience (seeing a snake) is exposed with reference to another veridical experience (seeing a rope), but again, we are a priori sure that both cannot be true together. Then, the Buddhist skeptic, Vasubandhu, raises the ante with the question: could they not both be false simultaneously? The skeptical argument is premised on a denial of the realist thesis that experiences refer to a mind-independent reality. Vasubandhu’s argument for idealism appears right at the beginning of Vimśatikā, when he states: