But nowadays, as far as I can tell, no one believes in the existence of immortal spiritual substances except on religious grounds. To my knowledge, there are no purely philosophical or scientific motivations for accepting the existence of immortal mental substances.John R. Searle, The Rediscovery of the Mind, the MIT Press, 1992, p. 27
While I am intrigued by the following argument, I have never been quite sure whether to believe it. That is not because I find anything particularly wrong with it, just that it seems, well, too easy. As Robert Heinlein said, give a philosopher enough paper and he can prove anything. I am not interested in proving just anything. John Searle's statement above does still strike me as grotesquely false. But I would be happier if there were some dramatic phenomena that would vindicate the existence of souls, e.g. evidence of survival after death, transcendent existence, or supernatural powers, etc. Of course, many people believe that there is such evidence, but I have not encountered it personally. So for the time being, the following argument (from 1997/8) is, indeed, just an argument. Following it, however, are some more recent thoughts.
Why am I myself, rather than someone else?
This is a very basic question about life, but it may also strike someone as nonsensical. What would it mean for someone else to be me? Or, what would it mean for me to be someone else?
These questions, which are not easily addressed empirically, can be dealt with by way of thought experiments.
First, I can imagine someone else being me if a duplicate were to be made of my body, with all my features, memories, habits, etc., and then if I were to be replaced by it. This was essentially the plot of the science fiction movie The Invasion of the Body Snatchers (1956, 1978), although the duplicates in those cases were not precise copies of the replaced individuals -- they were actually alien beings that were duplicates to all external appearances, but not internally. However, it is not hard to imagine true duplicates being made, especially with the kind of technology imagined for the transporter machines in the Star Trek television series. The 6th Day, a recent Arnold Schwarzenegger movie (2000), was about just such complete duplicates. Nature itself produces duplicates, but only in the very first stages of life: Identical twins are genetically the same, but their experiences and memories begin to diverge as soon as the individuals start to develop separately -- something already happening in the womb. A true duplicate of an adult would require a mapping of every atom in the body, which can now more or less be done with Nuclear Magnetic Resonance Imaging (NMR or MRI) technology, and then a duplicate set of such atoms being assembled in precisely the same way, something rather further from present technology. This would not be a "clone," as presently understood, since a clone is only genetically identical. A clone would not have the same memories as the original individual, and it would be no more and no less like the original than an identical twin would be.
Could I be replaced with such a complete duplicate -- every atom, not just genetically identical -- it would think that it was me. But clearly it would not be me, especially if I were not destroyed in the replacement and continued to exist off somewhere else. We can imagine that such complete identity might produce a being that would simply see itself as existing in two places at once, but this would require some kind of communication; and that would require the existence of some kind of extrasensory or paranormal connection between the two bodies, which is not now part of established science. Without such paranormal communication, the identical individuals would each think of themselves as the original individual, although only one of them would be right; and they would immediately begin to diverge as individuals because of differing experiences.
So what would be the difference between the two individuals? Well, they would exist in different spatial locations, and they would consist of different, albeit identical, atoms -- and it is a postulate of quantum mechanics that all particles of the same kind are absolutely identical. I know what it would mean for me not to be that other individual, since it would not be part of my consciousness. However, what if I were to be instantaneously destroyed and replaced with that individual, so that there was, to all appearances, a spatial continuity between us, and a material continuity since, as noted, identical material particles really are identical (there is, according to quantum mechanics, absolutely nothing about them that would enable us to tell them apart). If that individual would still not be me, then there would have to be something else about me that makes me myself apart from physical content, memories, and spatial continuity. In other words, I can perform the thought experiment that would remove "me" from my body, leaving behind an individual that looked, thought, and felt like me, but was not. It would simply not have my consciousness, but another one, which could then ask over again why it is itself and not someone else.
This same kind of thought experiment can be run the other way around: What would it mean for me to be someone else? I can easily imagine suddenly waking up and having another body. Franz Kafka wrote a famous story ("The Metamorphosis," 1915) in which someone wakes up and has turned into a cockroach. I can also imagine suddenly losing my memory and not remembering who I am. This actually happens to people occasionally. It is also possible to imagine, as in the science fiction movie Total Recall (1990), that the memories of a different person have been put into me, and I wake up, not just not remembering who I am, but actually thinking that I am someone else. Combining these would produce a very dramatic effect: I might wake up both with a very different body and thinking and believing that I am a very different person. If this left me with at least the same brain, however, we would have no difficulty imagining how this could still be "me" in some accountable sense -- it would still be my brain regardless of how the body around it might change or what kind of memories might be scrambled or reprogrammed in it. Interestingly, however, our own brain is usually something that we never experience; so were body and memories to be changed, it would be difficult to verify our personal continuity short of neurosurgery. From an internal point of view, and an external one for most practical purposes, everything would be different.
Now if I imagine body, memories, and brain to be replaced, then it would be easy to say that the result could not possibly then be me. However, it is still possible to imagine that the resulting individual could be me, and this act of imagination has actually occurred in multiple world religions for centuries: it would still be me if it were the same immaterial soul. Thus, if I were to believe in reincarnation, I would actually think that I have been innumerable different persons in the past, all with different bodies, memories, and brains. As Krishna says to Arjuna in the Bhagavad Gita: "I have been born many times, Arjuna, and many times has thou been born. But I remember my past lives, and thou has forgotten thine" [4:5, Juan Mascaró translation, Penguin Classics]. Krishna, implies, of course that memories of past lives are retained by the soul. This is not necessary to the thought experiment. It is possible to imagine a soul that does not carry memories but still carries an identical consciousness that would distinguish Arjuna from another individual physically and mentally identical. Since Arjuna (and most of us) does not seem to remember any past lives, this is what is given in experience anyway.
What the thought experiments demonstrate is a truth of metaphysics that the same attributes can belong to different individuals, or in other terms that an individual as an individual cannot be exhaustively defined by abstract predicates. Thus, bodily features, memories, personality, etc. cannot uniquely determine an individual; so I cannot identify myself as an individual by any such qualities. This metaphysical principle has only been disputed by philosophers like Leibniz, who postulate the identity of indiscernibles, that individuals that cannot be told apart are actually the same individual. But such a postulate only works for Leibniz because he denies the existence of space, which can serve to distinguish otherwise identical individuals.
The spatial separation of otherwise identical individuals also can be interpreted to mean that the individuals consist of different quantities of matter. To philosophers as diverse as Aristotle, Descartes, Spinoza, and Schopenhauer, different space and different matter are ontologically identical conditions: Space itself, in effect, is matter. This may now be restated in terms of quantum mechanics: If identical subatomic particles are postulated as absolutely identical by quantum mechanics, then spatial separation, again, is the only thing that individuates identical particles as materially different.
In the thought experiments on my personal identity, spatial or material difference might seem to do the job. An identical copy of me would be spatially and materially different, and if I were replaced by an identical copy, however quickly, it is still possible to imagine that it is materially different, even if instantaneously placed in the same space. However, such a transference would result in no externally ascertainable difference whatsoever, which sounds somewhat paradoxical if were are to say that the "matter" is different. In these terms "matter" must actually be defined in such a way that it is not materially or empirically distinguishable from other matter. Another postulate of quantum mechanics is that if two things cannot be in principle distinguished, then they are the same thing. The only thing that can distinguish identical particles is their spatial location. Thus, if we say that two individuals consist of identical particles and cannot be spatially distinguished (because they are temporally contiguous in the same space), quantum mechanics would then judge that they are the same individual. That there would be a temporal difference doesn't help, since there is no empirical criterion by which it could be determined whether the "matter" has been switched from one moment in time to another or not. The only way in which we could then say that an identical individual could replace me instantaneously in the same space and still not be me is to require that there be a form of "matter" that is not accessible to physical science. A form of "matter" not accessible to physical science, however, would not be "matter" in any familiar or common sense meaning. An immaterial substance standing in the place of what we would ordinarily call "matter," however, would more easily be called the "soul."
If quantum mechanics loses track of matter by only using space to individuate identical particles, the thought experiment of me becoming a different individual contrariwise loses track of space and is only able to use matter for individuation. Thus, I can imagine instantaneously acquiring a different body, different memories, and also finding myself in a different place. If that is nevertheless still me, with my consciousness, it would have to be because the "matter," or the substantial substrate of my self, was moved to that new location, even if nothing else moved by way of the contents and characteristics of my physical and mental identity. Since such "matter" would then be inaccessible to physical science, it would be reasonable to call such a substantial substrate "immaterial"; and an immaterial substance would reasonably be the "soul."
It may help to recall what it would mean to say that I could find myself with a different body, a different mind, and in a different location and still be me. It would mean that the conscious existence that I experience now, the conscious existence that seems to disappear in sleep, and which I imagine, or suspect, or fear may simply become nothing in death, can still be imagined as the same conscious existence even if what appears in it is a different body, a different mind, and different place. Thus, I have not become nothing and can still be me, even if I seem to be someone else, cannot remember my old self, and have appeared in a different place. This conception of conscious existence as perfectly divorced from, and so possibly perfectly empty of, content first occurs in the Upanishads, especially the great Brhadâranyaka and Mândûkya Upanishads. Advaita Vedânta then concludes it is only the Self (Âtman) that has substantial, independent existence, while physical objects only exist as illusory appearances in consciousness.
Although "matter" in the senses examined, whether physical or immaterial, is a metaphysical conception that is not accessible to physical science, the device of thought experiments to examine these issues is a perfectly legitimate procedure, not only for philosophy, but even for physical science itself: Einstein's entire theory of Relativity was based on his own thought experiments. Thus, the basic question here, "Why am I myself, rather than someone else?" in no more dismissible than Einstein's question about what a light wave would look like if we were moving at the velocity of light with it. The paradox, however, of ending up with a definition of "matter" that abstracts from it all identifiable qualities was not lost on Buddhism, which rejected the idea of a substantial substrate to anything. Like Hume, Buddhism adopted a kind of empiricism where the very conception of substance, whether material or immaterial, did not qualify. However, that produced its own paradoxes, since Buddhism, like Hume, could not then account for the duration in time of objects or persons. Much of Buddhism accepted the doctrine of "momentariness," that individual objects do not abide for more than a moment, but this is considerably more paradoxical and counter-intuitive that the duration of a substantial substrate. What the Buddhist paradoxes show us is that the substrate, however intangible, is not an unnecessary hypothesis -- without it, as a synthetic ground a priori (as Kant would put it), the duration of individuals cannot be accounted for.
Instead, I must appeal to the doctrine of The Origin of Value in a Transcendent Function. Both kinds of "matter" are conceptions of "Negative Transcendence," the emptiness of existence over and above the phenomenal content of consciousness. Negative Transcendence has internal and external poles. External transcendence then corresponds to physical substance, which in terms of quantum mechanics, as we have seen, is functionally identical to space itself. Internal transcendence is then the substrate for the sense of personal identity that has been examined here in the "thought experiments on the soul." The question left open in The Origin of Value in a Transcendent Function was in what way internal and external transcendence corresponded to each other.
Now it appears that internal and external transcendence must in an important sense be independent of each other, since external transcendence, as space, cannot account for personal identity from an internal point of view, and internal transcendence, as the "matter" of personal identity, varies independently of space and what can be accessed by physical science. Thus, for there to be personal identity, there must be more than just space and external transcendence. Such a conclusion, however, does not produce a Cartesian Dualism of material and immaterial substances existing in the same logical space, for internal and external transcendence are kept ontologically apart. They are only united through "Positive Transcendence." Negative Transcendence, in other words, cannot be added as a transcendent object to the order of phenomenal objects. Transcendent objects are subject to the Kantian Antinomies. Rather than being added as a transcendent object to phenomenal reality, internal transcendence casts a "shadow" of Positive Transcendence on phenomenal objects: the numinosity of the self or soul in religious conceptions, or even just the "supernatural dread" associated with dead bodies or cemeteries.
The question, "Why am I myself, rather than someone else?" then, cannot be answered just with natural objects. It can only be answered with transcendence. But transcendence appears in the phenomenal world as the numinous quality of natural objects. This may be called the "soul." The soul, as an independent, transcendent object, however, cannot be said to be established by this argument. The fact that Buddhism rejects such an object is an important clue that it is subject to the undecidability of a Kantian Antinomy. There is no doubt, on the other hand, of the numinosity of persons in Buddhism, especially as they become Bodhisattvas and Buddhas, and of the reality of karma and reincarnation, despite the denial that reincarnation is the transmigration of a substantial self. Buddhist doctrine thus expresses the paradox of Negative Transcendence as an existence which nevertheless cannot be placed as an object in conceivable (i.e. phenomenal) reality. Later this would be conceived as the "Buddha nature" of individuals, an idea that, not surprisingly, set off controversy about whether this involved a "substantialist heresy" or not. It is, indeed, a fine line, although easily drawn with the theories of Negative and Positive Transcendence.
As noted, it is a postulate of quantum mechanics that subatomic particles in the same quantum states are absolutely identical in characteristics. Although many have believed that Einstein vindicated Leibniz's view of space, as relative, over Newton's, this feature of quantum mechanics decisively contradicts Leibniz, for whom space does not exist and objects that are indistinguishable from each other are identical to the same thing. But indistinguishable electrons are not identical to the same thing. They are distinguished form each other by their locations in space (although their possible locations may be summed in the wave function). Leibniz, of course, could respond that what makes the electrons different is their history, and their relationship to other objects. However, while Leibniz believed that his "monads" contained their history, and a representation of their relationships, within themselves, this is not the case for electrons. Indeed, quantum mechanics rules out any such things as "hidden variables." With an electron, what you see is what you get. And since Leibniz's monads don't actually interact with each other, the only terms of their history and their relationship with other objects are their motions and relationships in space. If space does not then exist, monads actually have no history and no relationships.
If we allow that identical objects, however, are distinguished by their locations in space, location in space will not work to account for identity. That is because, as an object moves, it comes to be at a different location. So if different locations serve to distinguish different objects, why does not a object become a different object by moving and coming to be in a different location? This poses a grave difficulty for the theories of matter in Descartes and Spinoza, where matter is all but indistinguishable from space itself. But space does not move around, while matter must move around, to maintain its identity. On the other hand, it is not clear that fundamental particles in quantum mechanics possess any "matter" in the traditional, substantial sense. Energy turns into electrons and positrons. Electrons and positrons collide and turn back into energy. What we see is a collections of attributes, or quantum numbers -- mass, charge, spin, etc. -- that looks like nothing so much as the "aggregates" (skandhas) of non-substantial existence in Buddhism.
Unfortunately, the denial of substance in Buddhism is intended to effect a denial of identity. If the problem is accounting for the identity of an object or sub-atomic particle from moment to moment, Buddhist metaphysics is specifically designed not to do this. The result is an effective thought experiment in what is required for identity: The "aggregates" are not enough. If an electron has an enduring existence, something has the mass, charge, spin, etc. that characterize it. And if the electron, as electron, ceases to exist, neither Parmenides nor Democritus would be surprised to learn that it does not simply become nothing. Mass/energy is conserved, and there are particles that carry them away. Matter will not be a Cartesian fixed quantity of "stuff" that no transformation can alter, but it will represent a durable continuity of identity, which carries the quantum attributes and can merge with other objects or itself divide into new objects.
This, indeed, is more an Aristotelian than a Cartesian view of matter. Perhaps the only difference is that Aristotelian matter only accounts for different individuals of the same kind. Something unique of its kind (sui generis) doesn't need matter and can exist as pure form (like God or the celestial intelligences). In the argument here, however, material substance does not merely account for different things of the same kind, or for different individuals that are otherwise identical in every way, but also for the identity of anything with itself from moment to moment -- and Aristotle's substance (ousia), after all, was in the form, not the matter. A Buddhist analysis of Aristotle's God would be that it has no self, no identity, and duration. Probably not what Aristotle wanted to say, but then he is vulnerable to the critique, since for "substance" he can only offer attributes, i.e. the form.
While Aristotle thought of form as substance, it might be noted that a curious thing happened to the terminology in the translation from Greek to Latin. Ousia is from the participle of the verb "to be" in Greek. Thus, it looks rather like essentia, "essence," in Latin, which is from the infinitive of the verb "to be" (esse). Substantia, "substance," itself, is entirely different, meaning to "stand under." There is a word that means "stand under" in Greek, and that is hypokeimenon. Aristotle does not use that synonymously with ousia. He applies it, as it happens, to matter. Perhaps it would be better to translate ousia as "essence," in which case we could take substance, the underlying thing, as always being what Aristotle associated with matter. His reluctance, however, is understandable, since he thought of matter as mere power or potential, which would disappear in God. By the time we get to St. Thomas, of course, that idea of a powerless God was unappealing.
If our concern then becomes personal identity, will the identity of material substance account for that? As I have argued, no. In physical terms alone, we know that there is a turnover of matter in our bodies. I believe that after 20 years or so, all the matter in our bodies is supposed to be different. A defendant in a legal case once even tried to argue that he was literally not the same person who had committed the crime, some twenty years plus in the past. His argument was not allowed as, indeed, we trace personal identity across that transformation. With the material objects, this can indeed produce some paradoxical results. The Stoics noticed that in their day the ship kept at Athens, which was supposed to have born Theseus to Crete, had finally been repaired so much that every single plank and other part of it was no longer original. Was it the "same" ship? In a way yes, and in a way no. With material objects, the less the original material, the less it is the original thing. There is no such ambiguity with people. And we can ask them.
Similarly, we can use the thought experiments detailed above. We can think of ourselves persisting even through transformations in body, memories, and everything else. We can even, as it happens, think of ourselves persisting through absences of consciousness. Indeed, we do that every day, as we awake from sleep. This would be challenging for Descartes, for whom the soul was essentially thinking, or for Advaita Vedanta, where the self (âtman) is essentially conscious. But it is not really a problem -- consciousness is not essential to identity when the identity of consciousness from moment to moment must itself be accounted for. If personal identity requires a substantial substrate different from material existence, our word for it would be "soul." This would be a different and more fundamental meaning for it than what soul was for the Greeks, the life force, or for Descartes, consciousness (Searle's "mental substances").
The remaining problem would be the epistemological one of why we believe there are substances at all. Not only Buddhism, but Berkeley and then, especially, Hume point out that since substances are behind or beneath everything we experience, we are not directly acquainted with them as such. So what is our evidence that there are such things? The Kantian argument of the "possibility of experience" is then that "substance" is a category, like causality, which is an a priori expectation about experience, not something deduced, derived, or proven from it. Our expectation that the existence of objects is durable, separable, and identical is the principle of "substance" by which we organize and understand experience. While Hume himself said that all reasonings about matters of face are based on the relation of cause and effect, it is obvious enough that many such reasonings are also based on the persistence, independence, and identity of substance.
What Kant would ask, of course, is what we can know about a substantial soul outside the limits of a possible experience. The soul, after all, is not a natural or phenomenal object, and it is difficult or impossible to imagine how it can exist, as a substance, in the phenomenal world. Kant's answer then is that the limits of possible experience represent the limits of our knowledge of objects, so that we do not know how it is that substantial souls can exist. An immortal soul, which would be immune to the slings and arrows of man and nature, is in that regard an unconditioned reality, the sort of thing that does not appear in phenomenal existence, either for Kant or Buddhism. Yet even Buddhism does not deny that there are unconditioned realities -- most importantly Nirvana. Thus Buddhism, which is ultimately neither materialistic nor naturalistic, actually has more in common with Kant than it does with Hume or, for that matter, John Searle. The soul as a numinous reality, is fully present in the numinosity of the Buddhist Arhat, Bodhisattva, and Buddha. This is no comfort for the materialist, the skeptic, or the nihilist.