 First, in the case of at least some members of our species, total brain failure is not necessary for death. After all, human embryos and early fetuses can die although, lacking brains, they cannot satisfy whole-brain criteria for death (Persson 2002, 22–23). An advocate could respond by introducing a modified definition: In the case of any human being in possession of a functioning brain, death is the irreversible cessation of functioning of the entire brain. While this may be practically useful in the world as we know it for the foreseeable future, this definition is not conceptually satisfactory if it is possible in principle for some human beings with brains (that is, who have functioning brains at any point in their existence) to die without destruction of their brains. The “in principle” is important here, for this is not possible in our world currently. But suppose we develop the ability to transplant brains. (The thought-experiment that follows appears in McMahan 2002, 429.) Recall that the whole-brain standard is generally thought to receive support from an organismic definition of death. But such a conception of human death, one could argue, only makes sense on the assumption that we are essentially human organisms (see discussion of the essence of human persons in section 2.1)—as some proponents explicitly acknowledge (see, e.g., Olson 1997). According to the present critique, the brain is merely a part of the organism. Suppose the brain were removed from one of us, and kept intact and functioning, perhaps by being transplanted into another, de-brained body. Bereft of mechanical assistance, the body from which the brain was removed would surely die. But this body was the living organism, one of us. So, although the original brain continues to function, the human being, one of us, would have died. Total brain failure, then, is not strictly necessary for human death. A possible rebuttal to this challenge from one who accepts that we are essentially organisms is to argue that the existence of a functioning brain is sufficient for the continued existence of the organism (van Inwagen 1990, 173–174, 180–181). If so, then in the imagined scenario the original human being would survive the brain transplant in a new body. Thus, the rebuttal concludes, it is false that a human being could die although her brain continued to live.