The failure of theories of personhood.

The belief persists in philosophy, religion, science, and popular culture that some special cognitive property of persons like self-consciousness confers a unique moral standing. However, no set of cognitive properties confers moral standing, and metaphysical personhood is not sufficient for either moral personhood or moral standing. Cognitive theories all fail to capture the depth of commitments embedded in using the language of "person." It is more assumed than demonstrated in these theories that nonhuman animals lack a relevant form of self-consciousness or its functional equivalent. Although nonhuman animals are not plausible candidates for moral personhood, humans too fail to qualify as moral persons if they lack one or more of the conditions of moral personhood. If moral personhood were the sole basis of moral rights, then these humans would lack rights -- and precisely for the reasons that nonhuman animals would.