Some people are clear about what they want from living forever: to not die, at all, at any point—to just keep going without end. However, sometimes people use the term ‘forever’ more loosely. A small ad that says ‘cute puppies seeking their forever home’ would not expect the lucky owner to still be looking after the dog when the Sun expands to swallow the Earth seven and a half billion years from now. In theory, people might live centuries or millennia or more if immune to ageing and disease. Actual lifespans would also likely be wildly varied, with some people dying while mountain climbing in their teens, and others making it to a ripe old age of five thousand. Imagine that a great scientist, Professor Vitalonga, offers you eternal life. Philosophers distinguish between two quite different meanings of ‘identity’, and we need to be clear which one we are talking about.