 The first version goes like this. (Wiggins 1968 contains the first appearance of this version in present-day philosophical literature; an equivalent puzzle is that of Dion and Theon, see Burke 1995.) Suppose a cat, Tibbles, is sitting on a mat. Now consider that portion of Tibbles that includes everything except its tail – its “tail complement” – and call it “Tib”. Tib is smaller than Tibbles so they are not identical. But what if we now amputate the cat’s tail? (A time-reversed, or “growing”, version can be considered in which a tail is grafted on to a tailless cat; the same responses considered below will be available, but may differ in relative plausibility.) Tibbles and Tib will now coincide. If Tibbles is still a cat, it is hard to see by what criterion one could deny that Tib is a cat. Yet they are distinct individuals, since they have different histories. But there is just one cat on the mat. So they cannot be distinct cats. They must be the same cat, even though they are distinct individuals; and so identity under the sortal concept cat must be a relative identity relation.