Carl Cohen and marginal cases

Anyone who wishes to include all human beings within the moral community while excluding all non-humans is faced with a problem. Whatever standard one chooses as the criterion for admission to the moral community -- rationality, moral agency, autonomy, ability to communicate, emotion, the ability to feel pain -- many humans score no higher, and some score lower, than some animals. Because of this overlap, it appears that to be logically consistent one must either exclude some humans from the moral community or else admit some non-humans. This is called the argument from marginal cases.

One response to the argument from marginal cases is what has been called the argument from species normality. This has been advanced by Tibor Machan, who says that a broken chair may not be good for sitting on, but it is still a chair and not a monkey or a palm tree. In other words, humans who are deficient in some key respect are nevertheless members of the human species and ought to be treated the same way as other members of their species. Perhaps the best-known defender of this position is Carl Cohen, in his article "The Case for the Use of Animals in Biomedical Research" and in his slugfest with Tom Regan in The Animal Rights Debate. Cohen says that while moral agency is key to membership in the moral community, this standard is not a test to be administered on an individual basis, but applies to all who are of the same kind. Humans are the kind of beings who have moral agency.

Nathan Nobis argues that Cohen's position has absurd and contradictory implications. David Graham takes issue with Tibor Machan.