Argument from marginal cases

The argument from marginal cases (also known as the argument from species overlap)^[1] is a philosophical argument within animal rights theory regarding the moral status of non-human animals. Its proponents hold that if human infants, senile people, the comatose, and cognitively disabled people have direct moral status, non-human animals must have a similar status, since there is no known morally relevant characteristic that those marginal-case humans have that animals lack. "Moral status" may refer to a right not to be killed or made to suffer, or to a general moral requirement to be treated in a certain way.^[2]

Although various cases are made for it, Raymond Frey has described the argument from marginal cases collectively as 'one of the most common arguments in support of an equal value' of animals' lives.^[3]