Abstract
How should we count people who have two cerebral hemispheres that cooperate to support one mental life at the level required for personhood even though each hemisphere can be disconnected from the other and support its “own” divergent mental life at that level? On the standard method of counting people, there is only one person sitting in your chair and thinking your thoughts even if you have two cerebral hemispheres of this kind. Is this method accurate? In this paper, I argue that it is not, and I advocate an alternative I call the Multiple Person View.
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Notes
See, for example, Zaidel et al. (1999).
(1984, p. 663).
(1984, p. 669).
Assuming that these half-brains are atomic, in the sense that they are not made up of parts that can themselves be disconnected and each support a mental life at that level.
Some say that the number of people to whom cooperating half-brains belong at a given time can depend on what happens later, but that position only seems worth considering if people have temporal parts, and the view that people have temporal parts is extremely controversial. Still, it ought to be addressed—but only after determining how we should count people assuming that they do not have temporal parts. Advocating the view that people have temporal parts are Heller (1990), Hudson (2001), Lewis (1976), and Noonan (1989).
See, for example, Unger (1990, p. 266).
In this case and in the related cases that follow, I ask the reader to assume that the recently deceased paralyzed and blind “individual” had a fully divisible cerebrum.
I ask the reader who seriously objects to the idea of half-brains that cooperate to support one mental life from different paralyzed bodies to imagine that, before making the half-brains temporarily cooperate, the surgeons transfer them to vats. With a little adjustment, the following arguments also apply to that version of the Contrast Case.
Unger (1990, p. 113).
I ask the reader who believes that two cooperating half-brains must be understood as supporting two mental lives that run in parallel to understand my arguments as being for the version of the Multiple Person View appropriate to that position, namely the view that two cooperating half-brains belong to two people with parallel mental lives. This view is endorsed in actual cases by Puccetti (1973, 1981, 1993) and, in imaginary cases, by Mills (1993). Puccetti believes that cooperating half-brains belong to two people because, on his view, that follows logically from the fact that such half-brains support parallel mental lives, which he believes is shown by consistent and convincing empirical data. Mills believes that cooperating half-brains support parallel mental lives because, on his view, that follows logically from the fact that such half-brains belong to two people, and he believes they belong to two people because, if they belonged to only one, personal identity could diverge from “what matters.” For the record, I doubt that the latter view is tenable. If personal identity cannot diverge from what matters, that must be in part because two cooperating half-brains belong to two people, not the other way around.
Unger (1990).
This is implied by his remarks on p. 140 of Shoemaker (1992).
If a divisible person can go from having two sets of psychological capacities to having one, why can’t an atomic person go from having one set to having two? Single Person theorists often state as fact that people have survived when a stroke has put one of their hemispheres out of action. If advances in neurosurgical technique enable specialists to put those hemispheres back into action, are we to believe such people must cease to be?
Multiple candidates cannot each continue to exist if there is only one resulting person. And in the Contrast Case it is arbitrary to claim that one of the candidates continues to exist rather than the other.
Can Single Person theorists retreat to the position that you exist during the intervening period, but not as a person? Not if, as many such theorists believe, we are essentially people. As Chisholm, for example, says, on his definition of a person “if an individual thing x is a person, then in every possible world in which x exists, x is a person from the moment it comes into being until the moment it passes away” (1976, p. 137). Moreover, since the fine neurological structure that underlies your psychological capacities is retained during the intervening period, your psychological capacities are preserved. And if someone continues to exist with the same psychological capacities, he cannot cease to be a person.
For a detailed discussion of what matters in the case of Division, see Parfit (1984, pp. 253–266).
Nor can (3) be defended as a consequence of the Single Person View. It is simply not credible to say that you stand in the relation that matters to the sole survivor of an explosion that destroys your half-brain and body at the end of the Contrast Case. If you know that the survivor will acquire some new and exciting knowledge—say, the truth about the assassination of President Kennedy—it is certainly wrong to say that you can reasonably look forward to acquiring that knowledge. And how can the relation that matters obtain between you and someone to whose experiences you cannot reasonably look forward?
I ask the reader to imagine that in this case the organism’s cerebrum is made up of cooperating brain-hundredths instead of atomic half-brains, and that each brain-hundredth had been transplanted into a different empty-headed body.
Doepke believes that there are three people after Division: two conscious people who each have one half-brain and a single body, and one spatially scattered, unconscious person who is made up of the other two (1996, pp. 253–254). See also Unger (1990, p. 265, n. 8). This suggests the view that there are three people during the intervening period of the Contrast Case: two unconscious people who each have one half-brain and a single body, and one spatially scattered conscious person who is made up of the other two. If we cannot affect the number of people simply by moving them from two bodies to two vats, from two vats to one, or from one vat to the empty skull of one body, the result of doing so must on this view be three people who inhabit a single body with two cooperating half-brains. And that many people must inhabit every such body, assuming that physically indistinguishable organisms in the same surroundings cannot differ with respect to the number of people who inhabit them. Are such bodies inhabited by three people, as opposed to just two? I do not believe so. Once we agree that at the end of Division there are two half-brained people each of whom exists and is a person at the start, what reason is there to believe that the start of Division also involves someone else? As I have said, Doepke believes that there are three people at the end of Division, and that suggests the view that there are three people during the intervening period of the Contrast Case too. That, I agree, would be reason enough. But Doepke’s reason for believing in three people at the end of Division is that Division involves one person at the start—one person who is incapable of intermittent existence and who would exist provided that his half-brains were fused after having been divided. And that reason for believing in three people at the end of Division cannot also be a reason for believing in three people at the start. We cannot conclude that the start of Division involves three people as opposed to two on the basis of an argument that assumes it involves only one. But see Perry (1972).
Johnston, for example, says, “So were we ever to face fission, it would be reasonable to care about our fission products as we would care about a future self. But this is not because identity is never what matters; rather, this is because caring in this way represents a reasonable extension of self-concern in a bizarre case” (1997, p. 170). He also says, “Identity is still almost always what matters” (1997, p. 172). A similar position is advocated by Sosa (1990) and Unger (1990). For the view that identity is never what matters, see Martin (1998), McMahon (2002), Nozick (1981), Parfit (1984), Rey (1976), and Shoemaker (1984).
For the record, I believe that personal identity must coincide with what matters. This position is also endorsed by Mills (1993) and Lewis (1976). However, it does not appear to be compatible with the rest of Lewis’s metaphysics of the person, as is demonstrated by Parfit (1976). Parfit is followed on this point by Mills (1993) and Sider (1996). Sider sees himself as defending a version of the view that identity is what matters, but he cannot endorse a literal version of that view because he does not believe that people exist over time, and I do not understand why he thinks it is worth trying to defend another version of it—especially if his defense requires saying that no one exists for longer than an instant.
The view that we are animals is advocated by Ayers (1990), Carter (1980, 1982, 1988, 1989, 1990), Merricks (2001), Olson (1995, 1997a, b), Snowdon (1990, 1991, 1995, 1996), and van Inwagen (1990). The costs of the view that we are our bodies are no lower, as can be shown by replacing “animal” with “body” in what follows. That view is advocated by Thomson (1997).
That the resulting person must be someone else is in fact held by Carter, Olson, Thomson, and van Inwagen. Snowdon is friendly to this view, but he does not fully endorse it.
Such examples assume for simplicity that a cerebrum can support a mental life after it is detached from the brain stem, and that assumption is contrary to what scientific research suggests. But there is no harm in making that assumption in this context, as Animalists agree. To the contrary, that assumption helps to highlight the great divide between Animalism and its competitors (Olson, 1997a, pp. 44–46). Moreover, once we understand this divide, we can better decide what to believe in actual cases. Indeed, we can scarcely claim that people without such detachable cerebrums (actual people) are animals, if we determine that people with them are not.
See the chapter “Why We Need Not Accept the Psychological Approach,” in Olson (1997a, pp. 42–72).
Ayers and van Inwagen are the only Animalists to consider the case of many-headed animals, but they both advocate this way of counting people. Others might insist that if each head of a two-headed animal contains a different (noncooperating) half-brain such animals should be counted, not as one animal who has two organs of thought, but as two animals who each have just one. But that implies that psychology—and not biology alone—is relevant to how we count biological organisms, and that cannot be plausibly maintained if psychology is irrelevant to how we identify them, as Animalists ordinarily say. One might reply that, while human people are human animals, human animals have psychological persistence conditions—persistence conditions that, for example, have them “go with” their organs of thought if they are transplanted into the empty skull of a new body. But, as Olson (1997a, pp. 109–123) demonstrates, this proposal does not appear to be tenable. And if we accept it, we lose immunity to my attack on the Single Person View.
But see van Inwagen (1990). On his view that many things compose a single thing just in case the collective activities of the many constitute a biological life, a “cerebrum-in-a-vat” cannot support the mind of a material person, since any such person must be a living organism, but no cell in the vat is a person, and there are no other organisms in the vat for a person to be. It is worth noting that this view is particularly uncomfortable in combination with the view that there cannot be thoughts or experiences without a subject, which van Inwagen also advocates (1990, pp. 209–210). If experiences must have a subject, and there is no subject in the vat, any suffering therein must be only virtual suffering. We therefore have no moral reason to prevent even the worst such suffering, and we are permitted to cause all the virtual agony we like.
Assuming as Animalists would that, between the animal and any former envatted person in its skull, there are not two people.
I welcome comments at howtocountpeople@gmail.com.
This might lead us to doubt that a disconnected right half-brain really does support its “own” mental life at the level required for personhood. See, for example, Eccles (1980). But Sperry explicitly says otherwise. Thus in response to a view that “concedes that the [disconnected] mute hemisphere may be conscious at some levels, but denies that…[it]…possesses the…type of awareness that…is needed, so it is said, to qualify a conscious system as a ‘person’,” he says, “All results to date support the conclusion that the [disconnected] right hemisphere, despite its language deficits, harbors a well-developed, seemingly normal conscious self with a basic personality and social self-awareness that is in close accord with the presurgical character of the patient and also with that of the speaking hemisphere of the same subject” (1984, p. 668).
The answer must be: because your half-brains have never supported their “own” mental lives or belonged to different people. But for reasons of the kind I give in Sect. 4, such answers are indefensible, assuming that physically indistinguishable organisms in the same surroundings cannot differ with respect to the number of people who inhabit them.
If a two-hemisphere person can survive the loss of a half-brain to stroke or injury, as Psychological Continuity theorists claim, a one-hemisphere person can survive the growth of one. A one-hemisphere person, we must therefore admit, can survive if the single half-brain that supports his mental life comes to be linked to a second half-brain to support a mental life.
MacKay and MacKay deny that disconnected hemispheres support two mental lives because they believe that “at the higher levels of supervisory evaluation [split-brain patients have] not two half-systems but one undivided system, presumably associated with deep neural structures not surgically separated” (1982, p. 691). But if there is one “undivided system” associated with deep neural structures that have not been separated, does that mean that there are two “half-systems” associated with these structures if they have been separated? If the answer is Yes, I ask the reader who is friendly to the MacKays’ view to understand my arguments as being for the claim that the cooperating halves of an ordinary cerebrum belong to one person only if they belong to one person after they and such structures have been separated.
Since either way agony would be experienced by the same person and no one else.
That we do not have the technology required for the transplantation of actual whole brains, or for such wireless control, does not in itself prevent us from asking and answering the question of how we should count people if we did. And we should not count people differently merely because we lack this technology.
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Acknowledgments
For useful comments on various versions of this material, I am grateful to Bernard Berofsky, W. R. Carter, Thomas Pogge, Peter Unger, Achille Varzi, Carl Voss, and an anonymous referee for this journal.
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Appendix
Appendix
As I have said, research in neuroscience suggests that, like the halves of fully divisible cerebrums, the halves of normal human cerebrums—ordinary cerebrums—cooperate to support one mental life at the level required for personhood even though each hemisphere can be disconnected from the other and support its “own” divergent mental life at that level. But ordinary cerebrums differ from fully divisible cerebrums in certain ways. The halves of fully divisible cerebrums contain duplicate sets of sophisticated psychological capacities and features. Thus the single psychology they cooperate to support can continue to be supported by either half, with little or no discontinuity, despite the loss of function of the other. But the halves of ordinary cerebrums differ in their abilities. Typically, for example, the left half can produce speech, but the right cannot, and the right half is also less sophisticated in other ways.Footnote 33 In addition, each half of a fully divisible cerebrum can support a mental life at the level required for personhood after being disconnected not just from the other half, but also from the brain stem. But neither half of an ordinary cerebrum can support a mental life at any level after being disconnected from the brain stem. Can these differences in themselves justify the view that the cooperating halves of ordinary cerebrums belong to just one person, if those of fully divisible cerebrums belong to two?
The answer depends partly on whether the disconnected halves of an ordinary cerebrum belong to one person who has two mental lives at the level required for personhood or two people who each have one. Say that they belong to two people: Lefty, a speaking person whose mental life is supported by the left half-brain; and Righty, a mute person whose mental life is supported by the right half-brain. Then it is only defensible to claim that the cooperating halves of ordinary cerebrums belong to one person if at least one of these two people ceases to exist upon the temporary reconnection of their half-brains. (If their cooperating half-brains belong to two people, how can yours belong to just one?Footnote 34) But that either person temporarily ceases to exist does not appear to be defensible.
We cannot, for example, claim that either person ceases to exist because there is insufficient psychological continuity for personal identity. For each person, the fine neurological structure that underlies his psychological capacities and features is retained, sufficiently preserving his psychological capacities and features. It is true that the psychology that results from the reconnection of each person’s half-brain is more sophisticated than Righty’s. But Psychological Continuity theorists do not claim that a person ceases to exist if his left half-brain is put out of action and the resulting psychology is less sophisticated. It would therefore be hard for such theorists to maintain that he ceases to exist if his left half-brain is put back into action and the resulting psychology is more sophisticated. And if he survives with a more sophisticated psychology (than when his mental life is supported by just one half-brain), why doesn’t Righty?
The difference, we might believe, is that Righty has a competitor to be the “single” person who results from the reconnection of his half-brain to Lefty’s, and in this competition, Lefty is the winner. But to defend the view that Righty ceases to exist, we cannot rely on the claim that just a single person results. That claim is not defensible unless Righty ceases to exist. And there does not appear to be another defense of the position that either original person ceases to exist. No such defense can claim of either Righty or Lefty that he ceases to exist simply because the single half-brain that supports his mental life comes to be linked to a second half-brain to support a mental life.Footnote 35 Any such defense must also involve the fact that the half-brain to which his half-brain is linked belongs to someone else beforehand. But it is not relevant that these half-brains belong to different people before they are linked, unless we assume that just a single person exists after they are linked, which we cannot do here.
It follows, I believe, that the cooperating halves of an ordinary cerebrum belong to one person only if they belong to one person after they are disconnected. But unless we deny what research in neuroscience suggests,Footnote 36 this must be one person who has two divergent mental lives at the level required for personhood. And how can two such mental lives, supported by the disconnected halves of an ordinary cerebrum, belong to just one person if one mental life, supported by the cooperating halves of a fully divisible cerebrum, belongs to two?
Consider, for example, the two people who inhabit the single body at the start of Division. If their half-brains are disconnected and each supports a different mental life from within the skull of the same body, one mental life, we must admit, belongs to one of the original people and the other mental life belongs to the other. Say that their whole brain, with its disconnected hemispheres (and its brain stem), is transferred to a vat from which each person controls and receives sensory input from a different (empty-headed) body by wireless signal. One person, let us say, controls a body like yours and has thoughts and experiences of the kind you are having now; the other person controls a body like mine and has thoughts and experiences of the kind I am having now. Suppose that because one of these bodies is about to be tortured, one mental life is about to contain agony. Then each person has a special reason to hope it will be the other’s body. Nor can it matter if each hemisphere is damaged and the person with a body like yours comes to have a mental life at the level typically supported by the disconnected left half of an ordinary cerebrum, while the person with a body like mine comes to have a mental life at the level typically supported by the disconnected right half. Again, we must admit, each person has a special reason to hope it will be the other’s body that will be tortured.
But the mental lives of these people are supported by the divisible hemispheres of an envatted whole brain, hemispheres that do not require the brain stem (to which they remain attached) to support consciousness. Can it make all the difference if these mental lives are instead supported by the ordinary hemispheres of an envatted whole brain, hemispheres that do require the brain stem (to which they remain attached) to support consciousness? Can it be true that if these mental lives are supported by divisible hemispheres, they belong to two people, each of whom has a special reason to care which body will be tortured, but if these mental lives are supported by ordinary hemispheres, they belong to just one person who has no reason to care?Footnote 37 And if we do not know how these mental lives are supported, can it be true that we do not know whether anyone has a special reason to care?
To these questions, I suggest, the answer must be No. It would be implausible enough to claim that these mental lives belong to one person either way. But to claim that in one case they belong to one person and in the other they belong to two is too much. It follows, I believe, that even if these mental lives are supported by the ordinary hemispheres of an envatted whole brain, they belong to two people. That is all-important. We cannot affect the number of people to whom these mental lives belong by severing the wireless connections that link each ordinary hemisphere to a different body, or by transferring the whole brain that contains each hemisphere from a vat back to the skull of the same body.Footnote 38 In the end, these mental lives must remain the mental lives of two people, albeit two people who inhabit one body. And if these mental lives belong to two people, any two mental lives supported by the disconnected halves of an ordinary cerebrum must belong to two people. But in that case, as I explained, even the cooperating halves of such cerebrums belong to two people.
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Bajakian, M. How to count people. Philos Stud 154, 185–204 (2011). https://doi.org/10.1007/s11098-010-9531-2
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DOI: https://doi.org/10.1007/s11098-010-9531-2