by J.S. Blumenthal-Barby, Ph.D.

In a recent article in New Scientist (http://www.newscientist.com/article/mg22530103.700-first-human-head-transplant-could-happen-in-two-years.html?full=true#.VRbZpUJ3XuV), Italian neurologist Sergio Canavero claims that the first human head transplant could occur as early as 2017. He plans to announce his project at the American Academy of Neurological and Orthopaedic Surgeons conference in June. Here I set aside assessment of the scientific and medical merit behind this plan (though it is of note that this procedure was performed on a monkey who lived for 8 days), and I also set aside assessment of the broader ethical issues associated with this idea, and focus more narrowly on the issue of personal identity—though personal identity is of course an ethical issue as well as a metaphysical one.

For those of us who are philosophers, the announcement garnered intrigue given that one of the world’s most well-known living philosophers, Dererk Parfit, has written extensively in the philosophical literature on this idea. In his early work, Reasons and Persons, Parfit aimed to work out an answer to the question of what makes someone the same person over time (i.e., the question of personal identity in a numerical sense). Options include the continuity of a metaphysical immaterial substance such as the soul, the continuity of the body or the human animal self, or the continuity of one’s psychological make-up or thinking self. Parfit favors a psychological continuity criterion for personal identity. What “matters,” really, is connectedness of memories, desires, intentions, etc. over time. Though I certainly have different memories and intentions at the age of 35 as I did at the age of 15, at each time point that led up to the present, there was overlap and connection between these memories, desires, beliefs, etc. And in fact, some have remained throughout all of these years (e.g., I still have the experience memory of being 10 and saying goodbye to my first friend who moved away), and no one else in the world has that psychological content and connectedness, and that is significant. Parfit goes on to argue that there is, however, no “deep fact” about personal identity such that the questions of whether Person A and Person B (or Person A at time 1 and Person A at time 2) are “the same person” or whether “I” survive or die if all of my psychological make-up were transferred to another body or a computer are in a way irrelevant questions. The relevant question—what we care about—is the continuity of our mental or psychological metaphysical narrative. That is why Parfit says that such a continuation would be “as good as” survival.

Part of what motivates Parfit’s psychological view of personal identity is a thought experiment about head transplants and what he calls “the transplant intuition” in his 2012 paper, “We Are Not Human Beings.” Here Parfit asks you to imagine that your body is fatally diseased but there is someone else whose brain is fatally diseased, and a surgeon grafts your head onto this donor’s body. Parfit believes that most of us would share the intuition that that would still be you, thus supporting the psychological view and serving as an objection to the body or human animal view. Parfit also thinks this intuition would hold even if it were only your head and cerebrum that are transplanted onto someone else’s body and brain stem.

There are, however, some difficulties or puzzles with this view. The view is essentially a view that we are our brains (as Parfit puts it, we are “the conscious, thinking, controlling parts of [human] animals”—the “Embodied Persons” view as he calls it). One problem with this view is what Parfit calls “the physical properties objection” best articulated by Eric Olson who Parfit quotes, “Is it really a serious view…that we are about four inches tall and weigh about three pounds?” Parfit responds that it is plausible that we can sometimes claim ourselves to have the properties of our bodies just as we sometimes claim ourselves to have properties of our clothes (when I say for example, “I have been splashed with mud” when my pants have). A second problem with this view, again articulated by Olson, is the “epistemic problem” that there are “too many thinkers” (i.e., the “person” that is thinking and the “human animal” that is thinking) and how do you know which one “you” are? Parfit’s response is to offer a distinction between “the Inner-I” and “the Outer-I” where the Inner-I is the person, the conscious, thinking, controlling part that is directly thinking a thought and the Outer-I is the animal that is indirectly thinking the thought by having the Inner-I part. When any direct thinker thinks it knows that it is Inner-I the person and not the animal—hence there is no epistemic problem.

Whether Parfit’s responses are sufficient enough to address the objections to the “persons” view such that in the case of head transplant, the person who wakes up with their head on a new body is still clearly the same person they were before, I leave as an exercise to the reader. The alternative, of course, is the view that there is something to the human animal view such that there is doubt as to whether that person would continue to exist after their head is transplanted onto a new body. Instead, what we would have is the other person (the donor of the body) who continues to exist and is psychologically just like the head person and mistakenly believes that she or he is them.