 Scepticism is an offshoot of science. The basis for scepticism is the aware­ness of illusion, the discovery that we must not always believe our eyes.…But in what sense are they illusions? In the sense that they seem to be material objects which they in fact are not. Illusions are illusions only relative to prior acceptance of genuine bodies with which to contrast them….The positing of bodies is already rudimentary physical science; and it is only after that stage that the sceptic’s invidious distinctions make sense.…Rudimentary physical science, that is, common sense about bodies, is thus needed as a springboard for scepticism…. (1975: 67)