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Recently I was watching the famous "Powers of Ten" video which starts with a

Recently I was watching the famous "Powers of Ten" video which starts with a couple at a picnic and moves out to the far edges of the universe, moving ten times further out each second. After this the camera goes back to the couple and enters the hand of the man at the picnic, moving through layers of skin, blood cells, molecules, atoms and finally a haze of interacting subatomic particles. What struck me about this part of the video is that if the camera was to move beyond the boundaries of the man's hand we wouldn't be able to tell. There is no demarcation between the subatomic particles which make up the man's hand and the subatomic particles which make up the surrounding air. So, in what sense do seperate entities exist? Is seperateness an illusion inherent to the experience of beings at a macroscopic scale, similar to our illusion that objects are "solid" when in reality an atom is comprised mostly of empty space?

I love that video! Thank you for your excellent question.

Of course, you are correct in saying that there is no sharp demarcation between the hand and its air around it. A water molecule that is part of the hand may at some point evaporate into the surrounding air. There is no particular moment at which the molecule leaves the hand and becomes part of the atmosphere. Its chemical bonds to other "hand" molecules weaken gradually, its distances from those molecules increase gradually, and even if these quantities do not change continuously (in the mathematical sense), there is no magic bond strength or distance at which the molecule officially leaves the hand and joins the air.

That being said, the fact that there is no sharp distinction does not guarantee that there is no distinction at all -- that "separateness is an illusion inherent to the experience of beings at a macroscopic scale". After all, there is no sharp distinction between night and day -- yet night is not the same as day. It may not be illusory to think that some molecules do not belong to the hand, some do belong to the hand, and some occupy an intermediate zone (a "gray" area). Separate entities can exist even if there is such an intermediate zone.

Moreover, in the course of solving a given physical problem, we might have to make more explicit what the difference is between the hand and its surrounding air. We might have to stipulate that a molecule belongs to the hand if and only if it feels a force greater than x towards the interior of the hand. Such a sharpened-up distinction may be somewhat arbitrary in the specific x chosen. But it might be serviceable for the purposes of a given physical problem. There might be a range of equally good ways of demarcating the hand from the air for the purposes of that problem. I'm not sure that such a case is best characterized in terms of separateness being "an illusion".

Let's say that I have a perfect duplicate who is psychologically continuous with

Let's say that I have a perfect duplicate who is psychologically continuous with me. If I get bad news from my doctor that my days are numbered, can I anticipate surviving my death?

A thought experiment akin to the one that you propose has been deployed by Derek Parfit, in his classic book, Reasons and Persons, which I highly recommend if you're interested in this topic, in order to argue that personal identity is "not what matters." According to Parfit--I'm simplifying somewhat--if some agent has a perfect duplicate who is psychologically continuous with the agent, then, according to Parfit, even if the agent dies, and therefore the agent's consciousness does not continue, and so s/he does not continue to exist (Parfit is therefore answering question to the negative, and admitting that you won't survive) what's important, namely one's plans, projects, etc., will be continued by the agent's duplicate, and that, again according to Parfit, is more important than the survival of one's consciousness--indeed, in such a case, one shouldn't be worried about dying, because what one values will be carried on (albeit only by a psychologically continuous duplicate of oneself). Now Parfit finds these considerations reassuring: are they? Is what matters to being the person that one is simply that one's plans, projects, etc., be continued? Consider the following extension of the thought experiment. Suppose that one is married, and that, unbeknownst to one's wife, one's perfect duplicate will take one's place upon one's death. Ex hypothesi, she won't be able to distinguish the perfect duplicate from the person with whom she shared her life up until that person's death and replacement by a perfect duplicate. Now suppose that she were to discover, somehow, that she is now living not with the person with whom she had shared her life up until the replacement, but with a replacement--albeit one physically and psychologically indistinguishable from the original: should she be unconcerned? Reflection on this question, may, I think, lead to a refining of one's intuitions regarding the importance of identity.

I have read an argument that states that if time is infinite, then we need not

I have read an argument that states that if time is infinite, then we need not worry about death because one day our DNA will return exactly as it was in this life. That is; 1 million ar a trillion years in the future, someone might come into existance with all my DNA (or to go even further into the future,further than we can perhaps imagine, this person may even go through the exact same life experiences I've been through) and this would be a reincarnation of me. Is this even a logical argument? what would make this future person me? I could clone myself now but that doesn't mean that I would experience the internal conciousness of my clone. Similarly, if someone mapped my brain, memories and genome and was somehow able to simulate me on a computer, would this be me?

I'm with you. I don't see any reason to suppose that some future person who happened to share your DNA would be you, no matter how similar the course of their life might be to yours. And that's even before we get to the question whether time in infinite (quite possibly not) and whether, if it is, it has the implications that this argument supposes.

The book "Philosophy through Video Games" contains an interesting discussion

The book "Philosophy through Video Games" contains an interesting discussion about the nature of personal identity, in relation to the claims video game players make about "themselves" and what "they" did while "in" a game. I wanted to ask the philosophers here what you make of a player's claim that, for example, "I shot two robbers yesterday in a video game." The player, as a human being, clearly did not shoot any other human beings or animals yesterday (one should hope), yet at the same time, saying the sentence is false seems like a gross oversimplification. Is a person's video game avatar an extension of their identity, and thus what happens to the avatar also (in a sense) happens to them? Or does the sentence use niche meanings of words rather than their normal meanings?

Before we make things complicated, let's try whether a simple approach might work. We can say that the "I" refers unproblematically to the agent as a human being and that the somewhat special meanings are those of "shoot" and "robber". These words have special meanings within the game just as "threatening your knight" has a special meaning in chess. To be sure, there's the difference that in video games -- unlike chess -- the player is "embodied" as some sort of virtual personality. So you can move "your" fist or cloak "your" body or lose "your" left arm. But how is this different from moving "your" rook and protecting "your" king or losing "your" queen in chess?

More interesting in your sense may be video games in which one creates a coherent personality. Perhaps you play a little girl and I play her grandmother. This is like collaborative fiction writing or improvization theater. In the end -- as with all good fiction -- one can debate about the psychology and motivations of such characters as well as about what they would have done if their situation had been different in some specific way. These are interesting issues that have been discussed for ages. But I don't think they have much to do with personal identity. However similar a fictional character may be to its author, the two remain distinct even if the fictional character is described in first-personal language. When Vladimir Nabokov writes, in his novel Lolita, "I want to be with her," the "I" refers to Humbert Humbert, not to Nabokov.

Is it moral for me as a transexual to expect others to treat me as female? Is

Is it moral for me as a transexual to expect others to treat me as female? Is this a basic right of self-identification or am I inappropriately impinging my will on others?

You mean the word "expect" in a normative sense, I take it. You are asking others to accept and respect your self-identification and suggesting to them that they ought to accept and respect it. So you are asking for more than a basic right of self-identification. Still, I think what you ask is reasonable and something we others ought to accept and respect much as we ought to accept and respect another person's (newly changed or old) religious identification, sexual preference or choice of lifestyle when such choices do not harm us or third parties.

Obviously, a choice like yours may be hard for some persons to accept -- a wife may find it hard to accept that the man she loved and married now asks to be treated as a female. But leaving a narrow class of such exceptions aside, I don't think you are asking too much. Many may find it difficult to express their acceptance and respect in an easy and natural way as any explicit expression may strike them as awkward for themselves and also for you. But I don't think you really ask for, or need, such an explicit verbal acceptance. In fact, it may be more accepting just to treat you as a female, as you say, as just another woman -- without making a big to-do about it. Yes, we can do this, and we should.

Are we us,or our brain? If someone put our brain in a diffrent body will we be

Are we us,or our brain? If someone put our brain in a diffrent body will we be the same person? When we say 'me' we mean our brain? Because our brain is responsible for every single thought and move we make. Kostas 16years old,Greece

Your question goes to the heart of debates about personal identity, and even goes back to the early modern starting point for those debates, the chapter on personal identity in John Locke's Essay Concerning Human Understanding. Much discussion about personal identity has turned on the question of whether personal identity is to be located in psychological continuity or in bodily continuity of some sort; if one is inclined to think that the identity of a person is to be identified with the identity of her brain, then personal identity does indeed seem to consist in bodily continuity.

Your question goes even further, for you wonder whether the brain is to be identified as the locus of personhood, so that a person just is her brain. One thing that this view has going for it is that it seems that all human persons have had--it's not clear whether we can know, without doing brain scans, that all human persons have brains--brains. So having a brain would seem to be necessary for being a human person. But is having a brain sufficient for being a person? It's not clear to me that it is. For one thing, if one takes a person to be an agent, capable of having long term goals and forming life plans, then many human beings with brains do not count as persons. Moreover, even if one thinks that personhood is tied to being a human being (and human beings certainly have brains), it's not clear that personhood consists essentially in the identity of one's brain: the rest of one's body, and even one's psychology, could also be bound up with being a human being. As for whether a person would be the same person if her brain were transplanted into a different body, I don't really know what to say. Assuming that such a transplant could be done, if the rest of the body helps to determine the nature of a person, as much as her brain, then merely transplanting a brain into a different body would not preserve the identity of a person. (Maybe if the body into which the brain was transplanted was relevantly similar enough to the first body, then identity might be preserved.) Even if identity just consists in one's psychology, only if one's psychology could be preserved when one's brain was transplanted into another body, would identity be preserved. But I hesitate to draw conclusions about personal identity on the basis of a consideration of this sort of science fiction scenario.

I myself am inclined to think that the brain is importantly related to personal identity, although this is only an intuition, and I'm not at all sure just what role the brain plays in determining personal identity; I'm not, however, inclined to think that a person just is her brain. But cashing out this intuition is a matter for further, deeper, reflection. (Much of the philosophical literature on personal identity is devoted to exploring just such issues: if you're interested in exploring further, there are numerous good, relatively introductory starting points. I recommend Amelie Rorty's anthology, The Identities of Persons, and John Perry's Dialogue on Personal Identity and Immortality.)

Let's say I'm a mad neuroscientist who successfully alters the structure of a

Let's say I'm a mad neuroscientist who successfully alters the structure of a person's brain so that they end up with a completely different personality and memory set. Have I killed this person? Should I be tried for murder?

Yes. Of course, I only think that because I think personal identity depends on continuity of memory and character traits, and I think memory and character traits are constituted by brain states. So, if you could somehow alter my brain enough to wipe out my memories (perhaps replacing them with some artificial set of memories) and change my character traits, you will have killed me. And if you did it knowingly and purposely, you have committed murder (i.e., the intentional killing of a person). But...

1. I'm not sure how our legal system would deal with it. I suspect there's something in our murder statutes that requires a dead body for a murder charge. We'd have to get our laws up to date with our science (and philosophy!).

2. Now, I've opened the door to some slippery slopes (or sorites arguments). How much of my identity does an evil neuroscientist have to mess up before he kills me. If he deletes 50% of my memories and changes half my character traits, has he killed me (killed half of me?)? What about 90%? Of course, real-life brain damage or disorders, such as amnesia, Alzheimer's, and vegetative states, raise similar questions about when a person passes away, even if the body hasn't.

In a recent response by Eddy Nahmias, he ended up talking about "the capacities

In a recent response by Eddy Nahmias, he ended up talking about "the capacities [which] are the grounds for personhood". That made me think about arguments on abortion. Some pro-life people argue that the important thing is not the capacities some being HAS, but those that it can COME TO HAVE in some specified way (e.g., a "natural" way, or a way that is grounded on that being's "essence"). And that, they say, is what makes every fetus a person, and what makes a temporarily unconscious human a person. Both have to undergo some CHANGE before they can display specifically human traits that are important for personhood. Now, I don't find this argument very persuasive, but I really do not have a good answer to it. Could you tell me what is the difference (if any) between a one week human fetus and an unconscious adult that makes the latter a person, but not the former?

These are really tough and fascinating questions, both about what capacities are and what persons are. I hope other panelists might add to what little I have to say. What I will say (briefly, and without checking to see what the relevant literature has to say) is that one way to understand capacities is this:

An object X has a capacity C to perform C-relevant functions or behaviors (C-stuff) if and only if X has a structural organization O such that, when X is in the appropriate circumstances, O allows X to do C-stuff.

For example, I have the capacity to multiply any two numbers 1-13 because some structure in my brain allows me to get the right answer when the circumstances arise (e.g., when I'm asked to multiply 8 x 9 and I am awake and paying attention, etc.).

Having a capacity to do C-stuff can be distinguished from having the potential to develop the capacity to do C-stuff. The potential might involve being in a position (both structurally and environmentally) to develop the relevant structural organization to have the capacity. I have the potential to learn Russian, but I do not yet have the capacity to speak Russian.

So, assuming that some complex organization in our brains is what gives us the capacities for self-awareness that I associated with personhood (in my earlier response you cite), we can see that most adult humans have these capacities and are hence persons, while no fetuses have these capacities and hence none are persons. Most fetuses have the potential to become persons (though about a quarter of fetuses end in miscarriages). Unconscious adults actually have the capacities for personhood because they have the structural organization in place; they just aren't in the appropriate circumstances for them to be exercised. Even while I'm asleep or under anesthesia I still possess the capacity (organization O) to do my multiplication tables. I just can't exercise those capacities. A fetus does not have the capacity to do multiplication tables, nor to does it have the capacity to reflect on mental states and consider its past and future, etc.

So, by my definition of persons, fetuses (though they are human beings) are not persons, while unconscious adults are (and dolphins and apes probably are). One can draw various ethical conclusions from this, and I won't do so here. But IF one thinks that being a person means that one deserves more moral consideration than having the potential to become a person, THEN (if one accepts my view) fetuses deserve less moral consideration than adults (and perhaps some animals).

For more on this issue, see here.

Is identity determined by your physical appearance or something like a "soul"?

Is identity determined by your physical appearance or something like a "soul"? If someone was to receive a brain transplant and be inside another body, would they really be the same person they were before even if they had the same thoughts, ideas, and memories? Would the new body with the same brain just be a fake duplicate?

This is a deep and interesting question, which goes to the heart of the topic of personal identity, and reflects a tradition that stretches back to John Locke's treatment of the topic in the Essay Concerning Human Understanding. A preliminary note is in order, however: most contemporary treatments of personal identity--and that of Locke as well--do not turn on whether personal identity is determined by the body (one's 'physical appearance') or the soul, but in terms of whether personal identity is determined by the identity of the body or the mind. (By framing the question in this way, philosophers who are agnostic about the existence of the soul, or thinking substance--like Locke--or who deny its existence--like many participants in recent philosophical debates on the topic, can engage it without having to take up the issue of whether there is such thing as a soul.) Interestingly enough, the kind of 'thought experiment' that you propose to illustrate your question is one that Locke himself considers and with which philosophers continue to grapple. But let's set aside Locke for now, since his own treatment of the issue is complicated by his own views about the point of personal identity and the nature of our knowledge, and focus on the question itself.

I'm not altogether clear about the case that you're proposing, so I'll present my own way of framing it. The issue that you are raising seems to be the following: if a person's brain is transplanted into another body--assuming, I take it, that a person's psychological life supervenes on her brain and so a person would continue to have the same thoughts, ideas, and memories despite the fact that her brain is 'housed' in another body--would the person be the same person as before? The answer to this question is: it depends. If one takes the identity of a person to be constituted by her psychology, that is, ,her thoughts, ideas, and memories, then she would be the same person, even if she was occupying another body. But if one takes the identity of a person to be constituted by the identity of her body--and, after all, we normally identify and reidentify people on the basis of their physical appearance--then one might maintain that the person is different. For when a person undergoes a fundamental change in her worldview--think, for example, of Paul on the road to Damascus--one might claim that that person remains the same person. (Of course, in the case just cited, the person in question didn't think that he was the same person after his conversion: Saul became Paul.)

Now in such a case, would the person be a "fake duplicate"? (I presume that you mean that the person after the transplant would be a "fake duplicate" of the person before the transplant, as in John Woo's movie Face-Off, in which the thoughts of one person are transplanted into the body of another--and vice versa, but let's set that complication to the side.) Well, if the person whose psychological life had been transplanted into another body knew of the transplant, she could try to 'pass' as that person, and she might be successful, especially if she knew enough about the thoughts, ideas, and memories of the person whose body she was occupying, since, of course, from the outside, the fact that a new psychological life was being housed in that body wouldn't be apparent. If, however, no such attempt at 'passing' was made, then I'm inclined to say that the person wouldn't be a "fake duplicate," but would simply be occupying another body.

Now my last remark indicates my sympathy for the idea that personal identity is constituted by psychology. However, since I'm not inclined to think that psychology can simply be transplanted into another body--either by transplanting a brain or by any other means--and since in fact I'm inclined to think that one's psychology may well be constituted by one's body, I'm drawn to the idea that personhood isn't constituted either by psychology or by the body but by both. (I believe, although I may well be mistaken, that this position is known as 'animalism' in the contemporary literature, and is distinct from positions that take personal identity to be constituted by identity of the body or by psychology.)

This is a fascinating topic, that continues to receive lots of attention from philosophers--and which figures in various movies, ranging from Total Recall to Face Off to Eternal Sunshine of the Spotless Mind to All of Me. If you're interested in pursuing the issue a bit more systematically, a very nice starting point is a dialogue on the topic by John Perry.

I have heard that some philosophers claim that "self is an illusion". What does

I have heard that some philosophers claim that "self is an illusion". What does this mean? And how could anyone subscribe to this strange, counter-intuitive belief?

The idea of the self that is called into question when it is claimed that the self is an illusion is the idea of a substantial, persisting, intellectual substance, such as the self of which Descartes, in the second of the Meditations on First Philosophy, claimed to have knowledge, and which the later Rationalist, G. W. Leibniz, took as one of the foundations of his philosophy.

One of the most famous Western challenges to such an idea is raised by David Hume, in A Treatise of Human Nature. In Book 1, Part 4, Chapter 6 of the Treatise, "Of Personal Identity," Hume characterizes the belief in a persisting self: "There are some philosophers, who imagine we are every moment intimately conscious of what we call our SELF, that we feel its existence and its continuance in existence; and are certain, beyond the evidence of a demonstration, both of its perfect identity and simplicity." To this view, Hume responds: "For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe any thing but the perception....If any one upon serious and unprejudic'd reflection, thinks he has a different notion of himself, I must confess I can reason no longer with him. All I can allow him is, that he may be in the right as well as I, and that we are essentially different in this particular. He may, perhaps, perceive something simple and continu'd, which he calls himself; tho' I am certain there is no such principle in me."

Now Hume's challenge to the idea of the self is based on his view that every idea--like the idea of the self--must be based on some impression (this view is sometimes called Hume's 'copy principle', because Hume thinks that every idea is a copy of an impression): on the basis of introspection, Hume claims not be able to find such an impression--"when I enter most intimately into what I call myself, I always stumble on some particular perception or other...". (Hume's view is not altogether idiosyncratic, or wholly dependent on his 'copy principle': in the Critique of Pure Reason, Immanuel Kant also challenges the idea that human beings can have empirical awareness of such a persisting self.)

Nevertheless, to stay with Hume, Hume doesn't deny that there is any sense to be made of the idea of the self: in "Of Personal Identity," he remarks that "we must distinguish betwixt personal identity, as it regards our thought or imagination, and as it regards our passions or the concern we take in ourselves." And in Book 2, Part 1, Chapter 5 of the Treatise, he says that pride produces the idea of the self.

Thus, although Hume denies the existence of the self as a metaphysical subject, he maintains that some idea of the self is requisite to account for the concern we take in ourselves. This suggests that some sense can be made of the self after all, but that the self cannot be taken to some entity that is the subject of all thoughts. One might even go so far as to suggest that Hume is laying the groundwork here for a notion of the self as something that is constructed, rather than discovered. It is the latter view that Hume and other Western philosophers who have challenged the coherence of the notion of the self, mean to be questioning.

(I have emphasized Western challenges to the idea of the self; such challenges are also an important part of Buddhist philosophy, about which I am not competent to comment; I will, however, note, that it has recently been plausibly argued by Alison Gopnik that Hume himself may well have known about Buddhism, and so may well have been aware about Buddhist challenges to the idea of the self when he formulated his own distinctive attack on that idea.)

Debate about the cogency of Hume's view continues. The contemporary philosopher Galen Strawson has argued, in Selves, that there must be a self and that this self may be known, pace Hume, on the basis of first-person experience. If Strawson's arguments are cogent, then there may well be a way to defend at least a version of common-sense, albeit without returning to the perspective of Rationalists such as Descartes and Leibniz.