The Traditional Arguments for the Empiricist Conception of Sense-contents: the Argument from Illusion
Probably everyone agrees that objects sometimes look (or sound or feel or taste or smell) different from the way they actually are. A wide variety of different types of case are cited as instances of this obvious fact. Some examples are: mountains look purple when they are not and the sky looks blue when there is nothing actually blue there; clearly defined objects look fuzzy to the short-sighted; different lights make objects look different colours, though the objects don’t actually change; distance makes objects look the wrong shape; a hot hand and a cold hand feel the same water as being of different temperatures; MullerLyre lines look different lengths when they are not; objects appear to be different shapes from different angles-e.g. a round penny from the side looks elliptical; science shows that physical objects are almost entirely different from how they appear.