Among those who adopt Aristotle’s definition of the human person as a rational animal, Patrick Lee and Germain Grisez argue that whole brain death is the death of the human person. Even if a living organism remains, it is no longer a human person. They argue this because they define natural kinds by their radical capacities (the capacity to act or the capacity to develop a further capacity). A human person is therefore a being with a capacity for rational acts, and an individual having suffered whole brain death no longer has any such capacity. I present two objections to the radical capacities argument: first, that it fails in defining natural kinds, and second, that it misrepresents Aristotle. Aristotle defines natural kinds not by their capacities but by their functions. A brain-dead individual, I argue, is still a rational animal, but an unhealthy one that is unable to function.

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