Like Singer, Regan wants to provide an argument for vegetarianism. Unlike Singer, Regan does not want to base his argument on utilitarianism. Instead, Regan thinks that animal rights are the way to defend vegetarianism. We can think of rights in three ways. A legal right is a right granted by a legal authority. A natural right is what people talk about when they think that there is a naturally given right that people (or animals) ought to have. A moral right is just the other side of a moral obligation or duty. If someone has a duty to do X for you, then you have a right to have them do X. Regan is concerned with rights of the second and third kind. Regean claims that Singer's strongest arguments in favor of vegetarianism are arguments based on animals rights. Specifically, it seems that animals have a right to life.
Why might we think that animals have a right to life? Regan thinks that although Singer is wrong to base his arguments in utilitarianism, there is something right about focusing on an animal's capacity for pain. Regan says that the capacity for suffering is the basis of a right to life, or a right to live. He notes even though some humans are non-rational, they still have similar capacities for suffering as non-human animals. Regan says that the reasons why we don't eat non-rational human beings apply to animals as well. Namely, we don't eat non-rational human beings because they have the capacity to suffer. This capacity to suffer is the basis of a right to life. Regan notes that a rights-based approach is better equipped to explain why we do not kill and eat non-rational humans better than utilitarianism, Kantian ethics and egoism (self-interest).