If someone with normal colour vision looks at a lemon in good light, the lemon will appear to have a distinctive property—a property that bananas and grapefruit also appear to have, and which we call "yellow" in English. As we all know, however, it does not follow from the fact that an object visually appears to have a certain property that the object has that property. To use an example dating back to the ancient Greeks, a straight oar half-immersed in water appears bent, but of course it does not have the property of being bent. Ordinarily we take for granted that lemons and so forth are as they appear, but in a philosophical mood one naturally wonders whether we are right to do so.