In an edition of the Journal of Applied Philosophy released this week, several academics discussed Peter Singer's influential theory of "speciesism" - the view that human beings are inherently prejudiced toward their own species over others.
The target article of the discussion, the transcript of a lecture given by Yale philosopher Shelly Kagan, offers what Kagan says is a refutation of Singer's notion of speciesism. Kagan, both an ethicist and metaphysician, considers in particular the moral ontology underpinning Singer's theory, and argues that Singer provides insufficient evidence to show that sentience is the morally relevant property that one should consider when evaluating the importance of different species' interests.
"…when a speciesist claims that it is more important to avoid human pain than it is to avoid animal pain - even pains of equal duration and intensity - Singer insists that this is mere prejudice: 'pain is pain' he tells us (Animal Liberation, p. 20). But what is the argument for this last step?..."
"…I do think we have to recognize that one would be hard pressed to think of anything other than intuition to support the claim that the line between sentience and nonsentience is a morally significant one…"
Kagan argues for a form of what he calls modal personalism - the view that what makes an entity morally more important is the modal property of "potential personhood" (i.e. the ability to become a person).
In a reply to Kagan, George Washington University bioethicist David De Grazia challenges the claim that potential personhood is grounds for giving moral status to an entity. De Grazia writes:
"…If a human being is not a person but would have been if not for some improbable accident that occurred when he was an infant, we may rationally regret his lack of personhood. But it is much less clear that the fact that he could have been a person constitutes a reason to regard him as having higher moral status than he enjoys just on the basis of his categorical (as opposed to modal) properties…"
Oxford ethicist Jeff McMahan objects to Kagan's characterisation of personhood on the grounds that it could potentially privilege those with more cognitive functioning than those with less cognitive functioning:
"…According to this understanding of modal personism, both non-persons that once had the potential to become persons and non-persons that actually have the potential to become persons are modal persons and presumptively have a higher moral status than non-persons that have never had the potential to become persons…It seems to imply, for example, that the interests of a mature human foetus matter more than the comparable interests of a severely cognitively impaired adult, provided that the latter's actual psychological capacities are not significantly higher than those of the foetus…"
Singer himself argues that Kagan has misconstrued his argument against speciesism, and quotes passages from Animal Liberation that Kagan appears to have omitted from his discussion. Interestingly, Singer compares Kagan's critique "to the view standardly put forward by proponents of a natural law ethic when defending their opposition to abortion and to euthanasia for profoundly intellectually disabled humans".