Do animals have rights? This is how the question is usually put. It sounds like a useful, ground-clearing way to start. Actually, it isn't, because it assumes that there is an agreed account of human rights, which is something the world does not have. On one view of rights, to be sure, it necessarily follows that animals have none. Some philosophers argue that rights exist only within a social contract, as part of an exchange of duties and entitlements. Therefore, animals cannot have rights. The idea of punishing a tiger that kills somebody is absurd, for exactly the same reason, so is the idea that tigers have rights. However, this is only one account, and by no means an uncontested one. It denies rights not only to animals but also to some people -- for instance, to infants, the mentally incapable and future generations. In addition, it is unclear what force a contract can have for people who never consented to it: how do you reply to somebody who says 'I don't like this contract'?