The idea of identity is beset with problems. Everything wears out in time. Parts get replaced. Do such changes affect the identity of the object? How about if we eventually change all the parts of the original object? ‘Vagueness: how do you stop sliding down a slippery slope?’ considers identity and time. Another good example is of a child, who is still a child a second later, and again another second later. Eventually he or she isn’t a child anymore. How can logic explain that? Such sorites paradoxes provide some of the most annoying paradoxes in logic. The issue here is one of vagueness, where nothing is straightforward.