The rare condition known as dicephalus occurs when (prior to implantation) a zygote fails to divide completely, resulting in twins who are conjoined below the neck. Human dicephalic twins look like a two-headed person, with each brain supporting a distinct mental life. Jeff McMahan has recently argued that, because they instance two of us but only one animal, dicephalic twins provide a counterexample to the animalist's claim that each of us is identical with a human animal. To the contrary, (...) I argue that in cases of dicephalus it is obvious neither that there is one animal nor that there are two of us. Consequently, the animalist criterion does not straightforwardly apply to cases of dicephalus. I defend an account of dicephalus that is both sensitive to the complexity of twinning phenomena and not inconsistent with animalism. In my view, dicephalic twins are a borderline case of the concept HUMAN ANIMAL. I conclude with some speculative remarks concerning the normative import (if any) of my claim that dicephalic twins are a borderline case. (shrink)

We defend the view that we are not identical to organisms against the objection that it implies that there are two subjects of every conscious state one experiences: oneself and one’s organism. We then criticize animalism —the view that each of us is identical to a human organism—by showing that it has unacceptable implications for a range of actual and hypothetical cases of conjoined twinning : dicephalus, craniopagus parasiticus, and cephalopagus.

In dicephalus conjoined twinning, it appears that two heads share a body; in cephalopagus, it appears that two bodies share a head. How many human animals are present in these cases? One answer is that there are two in both cases—conjoined twins are precisely that, conjoined twins. Another is that the number of humans corresponds to the number of bodies—so there is one in dicephalus and two in cephalopagus. I show that both of these answers are incorrect. Prominent (...) accounts of biological individuation, which treat the organism as an integrated whole, reveal that in these and other cases of conjoined twinning the ‘twins’ share a single human animal. This has a number of consequences for the debate about what we are. First, if animalism is true, individuals of our kind can be—and are—profoundly psychologically divided. Second, cephalopagus twinning does not divide animalism from its rivals, as has been claimed. Finally, animalists can reply to a vicious species of the ‘too many thinkers’ problem to which they are allegedly uniquely vulnerable. (shrink)

Brain transplants and the dicephalus (an organism just like us except that it has two cerebrums) are thought to support the position that we are essentially thinking creatures, not living organisms. I try to offset the first of these intuitions by responding to thought experiments Peter Unger devised to show that identity is what matters. I then try to motivate an interpretation of the alleged conjoined twins as really just one person cut off from himself by relying upon what (...) I take will be the reader's disagreement with Locke's conjecture that a dreaming Socrates and an awake Socrates are two distinct people. (shrink)

Various cases of conjoined twinning have been presented as problems for the animalist view that we are animals. In some actual and possible cases of human dicephalus that have been discussed in the literature, it is arguable that there are two persons but only one human animal. It is also tempting to believe that there are two persons and one animal in possible instances of craniopagus parasiticus that have been described. Here it is argued that the animalist can admit (...) that these are cases in which human persons are not animals, without forfeiting the title “animalist.” It is also shown that this is not only an option but also a well-motivated and plausible option for the animalist. Seeing this requires getting clear on what the word “we” should be thought to include in the animalist's claim that we are animals. Here animalism is defended against twinning objections by figuring out how to view the scope of the animalist's identity claim. (shrink)

What are you and I essentially? When do you and I come into and go out of existence? A common response is that we are essentially organisms, that is, we come into existence as organisms and go out of existence when we cease to be organisms. Jeff McMahan has put forward two arguments against the Organism View: the case of dicephalus and a special case of hemispheric commissurotomy. In this paper, I defend the Organism View against these two cases. (...) Because it is possible to devise more McMahanian-type cases, I also provide a more general solution to these kinds of cases. (shrink)

In this paper I will provide a hylomorphic critique of Jeff McMahan’s “An Alternative to Brain Death.” I will evaluate three puzzles—the dicephalus, the braintransplant, and the split-brain phenomenon—proposed by McMahan which allow him to deny that a human being is identical to an organism. I will contend thatMcMahan’s solution entails counterintuitive consequences that pose problems to organ transplant cases. A Thomistic hylomorphic metaphysics not only avoids these unwelcome consequences and provides solutions to the three puzzles but in doing (...) so allows for an alternative definition of death. Since McMahan has constructed his definition of death around his own metaphysics, alternative metaphysics, in this case a hylomorphic metaphysics, allow for an alternative definition of death. (shrink)

In this paper I will provide a hylomorphic critique of Jeff McMahan’s “An Alternative to Brain Death.” I will evaluate three puzzles—the dicephalus, the braintransplant, and the split-brain phenomenon—proposed by McMahan which allow him to deny that a human being is identical to an organism. I will contend thatMcMahan’s solution entails counterintuitive consequences that pose problems to organ transplant cases. A Thomistic hylomorphic metaphysics not only avoids these unwelcome consequences and provides solutions to the three puzzles but in doing (...) so allows for an alternative definition of death. Since McMahan has constructed his definition of death around his own metaphysics, alternative metaphysics, in this case a hylomorphic metaphysics, allow for an alternative definition of death. (shrink)

In this paper I will provide a hylomorphic critique of Jeff McMahan’s “An Alternative to Brain Death.” I will evaluate three puzzles—the dicephalus, the braintransplant, and the split-brain phenomenon—proposed by McMahan which allow him to deny that a human being is identical to an organism. I will contend thatMcMahan’s solution entails counterintuitive consequences that pose problems to organ transplant cases. A Thomistic hylomorphic metaphysics not only avoids these unwelcome consequences and provides solutions to the three puzzles but in doing (...) so allows for an alternative definition of death. Since McMahan has constructed his definition of death around his own metaphysics, alternative metaphysics, in this case a hylomorphic metaphysics, allow for an alternative definition of death. (shrink)