Animal rights advocates, or rights liberationists, believe that these basic interests confer moral rights of some kind on the animals, and/or ought to confer legal rights on them;[1] see, for example, the work of Tom Regan. Utilitarian liberationists, on the other hand, do not believe that animals possess moral rights, but argue, on utilitarian grounds — utilitarianism in its simplest form advocating that we base moral decisions on the greatest happiness of the greatest number — that, because animals have the ability to suffer, their suffering must be taken into account in any moral philosophy. To exclude animals from that consideration, they argue, is a form of discrimination that they call speciesism; see, for example, the work of Peter Singer.[2]