Whether you have a soul is a very old question, and the consensus has generally moved from yes to no. I, however, disagree, and will here present why I think we have a soul, and what I think this soul is.
My little case here will run in two steps. First I will argue for property dualism: That there exist mental and physical properties, which are not the same. In the second step, I will try to make the move from property dualism to full on substance dualism (i.e. the idea that we have a soul).
The Private Nature of Experience
I first want to point out a specific feature of mental experience, which is the private nature. I want to distinguish between two types of properties: Physical and mental. The difference between these two is who has access to them. Physical properties are public; with the right equipment you can determine the weight, size, shape, temperature etc. of an object. You can also do this with the brain, and measure activity in it. But there is something you cannot access, and that is mental properties. Mental properties are private, meaning that only you have access to them. These are the what it is likeness of being you; the way you experience the weight, color, shape etc. of an object.
The fact that this distinction exists is corroborated by the problem of other minds: That we can be uncertain whether other beings are conscious is because consciousness lies in mental properties, that are essentially private. This distinction should give us reason to expect the mental to be distinct from the physical.
Philosophical zombies
In extension of this, one might run an argument from the possibility of philosophical zombies against physicalism. The argument runs something like:
There is a possible world in which people look and act exactly like we do: Going to work, having brain states, writing books about consciousness etc. all without actually having conscious experience. These are what we would call philosophical zombies: Creatures that are physically identical to us, but without phenomenal experience. If these are possible, then it shows that mental properties are not identical with physical properties, and thus physicalism is false. This might be formalized as follows:
It is possible to have a properly functioning brain without consciousness
If it is possible to have a properly functioning brain without consciousness, then physical facts do not fully explain consciousness
If physical facts do not fully explain consciousness, then physicalism is false
Therefore
Physicalism is false
Here I mean, by a properly functioning brain, a brain in which the same sorts of physical states arise as in your brain. The first premiss, I think, is highly plausible, at least prima facie. As discussed above, we can make a distinction between physical and mental properties, which suggest that one can have physical state x, which produces conscious state y in my brain, but don’t in the world described above. There is no way you could test whether this would be the case, since the mental properties are private, but this only counts in favor of the argument, since our uncertainty about whether there is a connection only illustrates that there is a distinction.
Personal Identity
What I have tried to establish above is a sort of distinction between mind and matter: Mind cannot reduce to matter, but must somehow go beyond it. If this succeeds, however, that does not mean that dualism has been established, since the view of property dualism (that physical objects can have mental properties, that are not substances in themselves) still fits this distinction. Given this, we should favor property dualism, since it is more parsimonious in only postulating another kind of property, rather than another kind of substance. What reason is there, then, for postulating mental substance? I think that considerations about personal identity serve this purpose.
Realism about personal identity
First off, why would we want to be realists about personal identity at all? It might seem obviously true, that we persist through time, but I don’t actually think it is as obvious as it seems. You might think that you just have a kind of immediate access to this fact, but unlike qualitative experience, there is no immediate experience of persisting. You only perceive one moment at a time, and thus any inference to persistence through time is made through memory of immediately prior moments. So you might think that the only thing that is you, is the thing experiencing the exact moment that you are experiencing right now, and that any prior and posterior locus of experience is another person. This theory seems simpler than the theory postulating persistent persons, so what reason is there for accepting such persons?
A good reason might be intuition. I explained above how the intuition that we persist through time is defeasible, but this does not mean that it cannot provide evidence for the idea, anyways. You might not be able to derive with certainty, that you exist through time, from experience, but the seeming is very strong, and thus it provides defeasible evidence for the idea. I think that this is the bulk of the reason for accepting personal identity: It just seems so obvious.
Secondly, I want to challenge the idea that denying personal identity over time is simpler. I think that there is one thing that is certain, and that is that experience is happening. This, I think, is good grounds for postulating a person who is having the experience. I also think that it is extremely probable that there exist more moments than the one I am currently experiencing, and that in the next moment after this, there will be a person having very similar experience to me, from the perspective of my body. Now, if you agree with this, you have two options: This person is me, or it is not me. Denying that it is me would here seem the more complex option, since it postulates a person for every moment, instead of a single person.
Another consideration in favor of personal identity over time, is in terms of morality. Now, this point is only going to apply for people who accept moral realism (which is the majority of philosophers (PhilPapers Survey), although it is still a very contentious position). The point is that there are a lot of things, that are commonly accepted about morality, that seem to presuppose the persistence of persons. The main two things are desert and hurting one person in order to bring about good consequences for another. Desert seems to presuppose personal identity, since it is commonly held that in order for it to be permissible to punish/reward someone for a given action, it has to be them, that performed the action. If person A committed a murder, it would not be permissible to punish person B for it. But if persons do not exist over time, then person A at the time of the action would be a different person than the person A’ at the time of the punishment. Thus for desert to make sense, persons need to exist over time. Now the second point about hurting one person in order to bring about good consequences for another, is quite similar. There are many thought experiments that give a strong intuition about these sorts of cases, for example the hospital case about sacrificing one patient in order to save the lives of 9 others. Here the intuition is, that this is impermissible. This intuition, however, makes no sense, if persons do not exist over time. If patient P (the healthy patient), is not the same person as person P’ (the healthy patient at a later time), then there is no reason to prefer patient P’ over patient Q1 (one of the sick patients), Q2 (another of the sick patients), or any Qn. If this is true, however, then you should obviously sacrifice P, since both patient P’ and patients Q1-9 are distinct from P, and thus should have the same priority. All these examples, are examples of non-utilitarian considerations, and thus these would not apply to a moral realist, if they are also a utilitarian. This should be obvious, however, since utilitarians (put very roughly) consider people somewhat like “utility containers”. Thus whether person A or B experiences some utility doesn’t matter, as long as the utility is experienced.
These considerations, I think, give very good grounds for accepting personal identity over time.
The argument
With all this groundwork laid, we can continue on to what this has to do with substance dualism. The thing is, it is very hard to give a coherent account of what constitutes personal identity. I will try to argue against two large groups of accounts: Psychological continuity accounts and physical accounts. The first group claims that personal identity over time comes down to some sort of psychological continuity over time: That you have the same sort of psychological profile from one moment to another. This profile might change over time (for example, you might go from liking grindcore to disliking it), but this change has to be continuous, such that there is not a sudden jump from one profile to another. The other group of views are physical accounts. These claim that the persistence of persons comes down to some sort of physical relation. Your persistence might come down to the persistence of physical objects, like your brain, body, or the persistence of physical processes, like biological processes of your body (I will quickly add that I reject many of these, since I am a mereological nihilist, and thus I would deny that there are any objects, that could continue over time).
Imagine that you take a person P and cut their brain in half. You then transplant each part into a separate body, each with a corresponding synthetic half-brain, such that there are now two people Q and R, each with one half of P’s brain. Now consider the following question: Which one is P?
Let’s look at the two theories outlined above, and how they might try to answer this. First, there is the psychological identity view. This view would claim that both Q and R are the same person as P, since both would be psychologically continuous with P. This, however, seems wrong. If both are P, then Q is P and R is P. At the same time, it should be obvious, that Q and R are distinct persons, especially if you let them live different lives, that diverge. To illustrate this further, you could also say that they are not psychologically continuous with each other, since two things that are different at one time cannot be continuous over time, from that point. But if Q is P and R is P, but Q is not R, then it follows that P is not P, which is obviously false.
Now, as for the physical views, these also seem to run into some problems. There here seem to be three options: Both Q and R are P, neither Q or R are P, or only one is P. The first one falls prey to the same objection as above: It follows, if we assume that Q and R are distinct, that P is not P, which is contradictory.
There is also the option that neither Q or R are P. This would mean that P died when the brain was split. This seems like a plausible option, but this can be turned into a sorites case, by realizing that splitting comes in degrees. I expand on these in my post about the chicken and the egg, but i will set up a case quickly here. Suppose that you split P’s brain with a knife. You might then ask the question: When does P die? Is it when the knife touches P’s brain? Probably not. When it has cut 1 mm? When it has cut 3.79 cm? When it has 99.99% through the brain? It seems incredibly difficult to say when P dies, in fact I say that there is no point when P dies, at least no point determined by the physical facts. The physical facts about P’s brain, or the processes herein, are just not adequate to determine at which point P dies, even if you knew all of them. This option is thus not open to you, unless you accept a paraconsistent logic, where P can be neither dead nor alive, or both dead and alive, but that seems like a very big commitment for this case.
The last option is of course that either Q or R is P. Here we need first to set up criteria for how to determine which is P. This will depend on the specific theory, and will thus be beyond the scope of this (already long) blog post. I will thus just focus on a single, intuitively plausible view. The theory is that the half that survives is the half with the largest amount of P’s brain. If one half weighs 630 grams and the other 570, the one that weighs 630 grams belongs to (or is) P. This criterion has some intuitive pull, since you might think that if you cut out a small bit of brain from a person, you are just “splitting” their brain at a very unequal ratio. It, however, has several counter-intuitive consequences. First, imagine that the brain was split exactly in half. In this case either both Q and R would be P, neither would, or it would be completely arbitrary who would. All these options seem unacceptable, and thus count against this theory. The theory also has the consequence that a single fundamental particle can determine who is P, since, if there is an odd number of fundamental particles in P’s brain, the split might be made such that a single particle makes the difference. This, again, just seems completely unacceptable and unintuitive. It seems plausible that similar problems would arise for any kind of account referring to physical facts, although the whole logical space cannot be explored here.
I will now present my solution to the case: Substance dualism. My version is something like this: There exists two kind of substance: Mental and physical. Physical substance is quite familiar: It as quantitative properties, that are objectively observable. Mental substance has the first-person, qualitative properties of consciousness. A soul is then a completely simple instance of mental substance. Each soul has a single essential property, which is its specific identity, or haecceity. A given soul is simply defined by its “thisness”, and thus each soul is distinct and simple, avoiding vague cases of identity. A souls is then also the locus of consciousness, with accidental mental properties experienced by it. These properties are determined by physical states, by psychophysical laws, such that souls do not determine actions, but only experience them.
On this theory, the answer is quite simple: P is identical to their soul, and the half that survives is thus just the half that keeps their soul. If the soul stays in Q’s half, then P is Q, if it stays in R’s half, P is R, and if it stays in neither, P is neither. P cannot be both, since the soul, on my theory, is simple, and cannot be split. To say that P’s soul “stays in” a half, is of course metaphorical, since the soul is non-physical, and is thus not located anywhere. What is meant is that the soul stays connected to that half through psychophysical laws, such that that half can affect the soul, while the other cannot. I here anticipate the following objection:
“On this theory there is no way of knowing who is P, since which half is connected to P cannot possibly be detected. The theory thus fails to solve the problem.”
This objection is exactly right, but also misses the point entirely. It is right that there is no way of knowing who is P. The point of the case is not, however, to find a theory on which we can find out who is P, the point is to find a theory on which there even is an answer. The other theories discussed fail to give an answer to the question of who is P. The dualist theory, on the other hand, gives an answer (the half with the soul), although it does not help us in finding out, through observation, the answer. There is thus a distinction to be made between the metaphysical and the epistemological question of who is P. The metaphysical question is: “Who is P?”, while the epistemological question is: “How can we know who is P?”. There being an answer to the first question is a prerequisite for answering the second question. All the theories thus fail in terms of the epistemological question, but only the dualistic theory can answer the metaphysical question, and thus comes out on top.
The options
This still leaves the option of a Moorean shift: We have three mutually exclusive propositions:
Personal identity is real
If personal identity is real, it depends on substance dualism
Substance dualism is false
In the above, I have tried to argue for 1 and 2, and thus for rejecting 3. However, one might think that, for example, 1 is less obvious than 3, and thus 1 is to be rejected. This is a plausible move, but I do, however, not think that substance dualism is, on the face of it, very implausible. I thus think that the intuition for personal identity, as well as the arguments from personal identity to substance dualism, both are more plausible than the intuition/simplicity considerations in favor of rejecting substance dualism.
Interaction Problem
Now I will touch on a classic objection to substance dualism, namely the interaction problem. This problem may be stated as follows: “How do physical states influence/cause mental events, and vice versa (if something like libertarian free will is true)?” It is not hard to see the problem here. If mental substance physical substance are supposed to be radically different (as the substance dualist would say), how then, can these two types of substance causally interact? First off, it may be worth to notice that this is not strictly an objection, but rather an odd thing about the theory. This, however, does not mean that it cannot pose a problem for the theory, since it is going to be hard to accept a theory that you cannot make sense of.
More importantly, though, it is not just causation between mental and physical that is hard to explain; pretty much any kind of causation is hard to explain. Thus I do not see very much more trouble in postulating physical-mental causation, than physical-physical causation. Furthermore, on my theory physical states cause mental states, but not vice versa, and thus this theory is consistent with causal closure. Calling it psychophysical laws rather than mental causation, also seems to demystify it. It is not some sort of magical link between the mental and the physical, but just simply another “law of nature”.
This then pretty much covers my theory of consciousness, and some of the reasons I have for accepting it.