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Swinburne’s Separations

Sally Latham on Swinburne’s argument that you can exist without your body.

Oxford Emeritus Professor of Philosophy Richard Swinburne says that when he began his academic career in the 1970s, about 1% of philosophers were dualists – believing that the mind and the brain are different things – but now this has grown to a whopping 2%. In an age of neuroscience and materialism, dualism is an unpopular theory in philosophical circles, often seen as a relic of the age of Descartes (the Seventeenth Century), before we knew much about brains. Swinburne aims to champion this underdog with his most recent (rather complicated) defence of ‘substance dualism’ – the claim that the mind is a distinct entity that can exist independently of the brain; something non-physical that constitutes ‘me’. He uses some classic thought experiments about brain-splitting, along with some abstract logical principles, to show how certain scenarios we can see to be logically and metaphysically possible can only be so if we assume his type of dualism to be true.

Although it may not seem so, the following is a simplified and stripped-back version of Swinburne’s arguments, and for the full impact one should read his Mind, Brain, and Free Will, published in 2013. This is neither a critique nor a support of his view, just an attempt to get more people to think about Swinburne’s arguments.

The Terminology

Swinburne makes the distinction between logical and metaphysical necessities on the one hand and logical and metaphysical possibilities on the other. His aim is to move from the logical possibility of a mind’s existence without a body to its metaphysical possibility – that is, from the idea that a mind without a body is logically coherent, to the idea that it is realistically possible. This is a metaphysical possibility, he claims, because there is a non-physical element which constitutes ‘me’.

To see this, and before we get to the brain splitting experiments we’re all waiting for, we need to clarify some rather abstract terminology.

An event is metaphysically necessary if it must happen, whatever else is the case. An event is metaphysically possible if it could happen under some circumstances. Some metaphysical necessities (or conversely, metaphysical impossibilities) can be discovered just by thinking about whether the proposition expressing them is logically coherent – which means that these are also logical necessities (or impossibilities). The easiest way to discover whether a proposition is logically necessary is to see if its negation entails a contradiction. Something is logically possible if it is not discoverable a priori (i.e. through thought alone) to be metaphysically impossible. For instance, it is logically possible that tomorrow will be a sunny day, as to deny this proposition is not contradictory (even if it is false).

Sometimes we can easily see if something is a logical possibility or not. But when it is less obvious, thought experiments can be useful to move from fairly obvious logical possibilities to less obvious ones. For example, it is logically possible that there is more than one space, a space being defined as a self-contained collection of places. We can show this to be logically possible by imagining what a world would be like where there are two spaces. C.S. Lewis’s Narnia would provide the perfect thought experiment to demonstrate this logical possibility.

So, we know how to discover logical possibilities, but what of metaphysical possibilities?

For this we need another set of definitions. Following Saul Kripke in his book Naming and Necessity (1980), a ‘rigid designator’ is a word which always refers to the same object in any possible world, whatever happens to that object. Kripke believes that names are rigid designators: they refer to the same thing in every possible world. He contrasts them with ‘non-rigid designators’, which refer to an object only as long as it has some non-essential property. So for example, ‘David Cameron’ is a rigid designator, whereas ‘the present British Prime Minister’ is non-rigid, as it could refer to a different person in different circumstances.

However, as Kripke and Hilary Putnam both pointed out, we run into a difficulty with some rigid designators. We can pick out an object named by some rigid designator by virtue of normal superficial properties, such as surface appearance, but the object’s essence really underlies those contingent properties, and is a necessary aspect of what makes that object that object, so the name really refers to the thing named in terms of its essence. However, even a competent language user may be ignorant of the underlying essence a word refers to, and hence not fully understand what they are referring to when using it.

Swinburne’s Designators

Swinburne himself uses a modified version of one of Kripke’s examples, asking us to suppose that long before people knew the geography of the Himalayas, explorers named a certain mountain seen from Tibet ‘Everest’, and a certain mountain of a different shape seen from Nepal ‘Gaurisanker’, using these names as rigid designators of those mountains. The mountains are in fact one and the same, but the explorers, not knowing this, believed the names to refer to different mountains. Or Putnam’s example uses the word ‘water’. In the Eighteenth Century this word referred to the transparent liquid in our rivers, but people had no knowledge of its chemical essence as H2O. This ignorance of water’s underlying essence may have left those using this rigid designator unsure whether it applied in some situations. For example, could there be transparent, drinkable liquid that looked and tasted like water but was not water?

Swinburne calls such labels ‘uninformative designators’, meaning there could be cases where we do not know how to apply the term appropriately. Even a competent language user in the Eighteenth Century would not always know when to correctly apply the term ‘water’.

For a rigid designator to be an ‘informative designator’, as Swinburne defines the term, it must be the case that anyone who knows what the word means knows the conditions in which to apply it (or the words by which it is defined), if their faculties are in working order, they are favourably positioned, and they’re not subject to illusion. An example is the term ‘red’. If you know what the term means you can’t be wrong about when to apply it, if your eyes are working properly and you’re not subject to illusion. Swinburne argues that although ‘water’ in the Eighteenth Century was an uninformative designator, ‘H2O’ as used today is an informative designator of that substance.

Both Kripke and Putnam argued that ‘water is not H2O’ is not logically impossible, yet is metaphysically impossible: we could deny that water is H2O without logical contradiction, and yet, given that we have now found out that water is H2O it cannot be otherwise that water is H2O (anything that is not H2O is not water, and anything that is H2O is water). However, Swinburne claims that the idea that ‘water is not H2O’ is only a logical possibility if we don’t understand what the term ‘water’ really refers to. He then argues that if we replace uninformative designators with informative ones, then if we know a sentence is logically necessary, we can also know it is metaphysically necessary. For instance, if in the sentence ‘Everest is Gaurisanker’ we substitute for both terms an informative designator ‘A’ designating the rocky matter of that mountain, we get a sentence which is logically necessary, since effectively we would be claiming that A is A; and this also means that the identity of the mountains is metaphysically necessary – it has to be the case in all circumstances. The upshot is that if we use informative designators to come to a logical necessity, then we can also see that we have a metaphysical necessity. And this also works for logical to metaphysical possibility or impossibility.

So far we have made no mention of dualism, brains, minds, or souls, but the above distinctions are crucial to Swinburne’s arguments. If Swinburne can show that survival without a body is logically possible, he could then invoke informative designators to show that it is also metaphysically possible. And if this metaphysical possibility can be shown to work for something non-physical that is ‘me’ then the case for substance dualism is made. That final stage is going to require one more principle… but we will save that for later.

The Thought Experiments

We can at last now move on to thought experiments involving brain operations. Remember that the point Swinburne is trying to make is that it is logically possible for me to exist without the same body (that is, brain), or as it turns out, even without the same memory or character.

We are now discussing personal identity. There are (broadly) two main theories of what constitutes personal identity over time. The complex view of personal identity states that personal identity is analysable in terms of degrees of continuity, whether the emphasis concerning what continues is put on memories, character, or bodily matter (usually the brain). The simple view is that each person has a ‘thisness’ apart from their brain matter, memory or character, and this ‘thisness’ is what makes him or her a person, and continue to be the same person over time.

Swinburne argues for the simple view, and he does so by arguing that it is logically possible for some person P2 at time T2 to be the same person as person P1 at time T1 without this identification relying on any continuity of memory, character, or brain matter. The way he demonstrates this logical possibility is to tell a story. The story may be familiar to some readers already, but it is not usually used to come to the conclusions that Swinburne comes to.

We’re told by neuroscientists that much of the same information is contained in both halves of the human brain. It is theoretically possible that my brain could be split into its two hemispheres, and transplanted into two new bodies. Furthermore, these new bodies could be clones of my body, so that each half-brain of the original ‘me’ is fused with its alternate half in a body that is a clone of my body.

Let’s call the original me C, and the two resultant people A and B. A and B each have half my original brain and half my cloned brain. At the moment of waking after the operation, A and B have identical bodies (apart from their brains), and supposing largely the same information in both halves of my original brain, they will both have the same character and continuity of memory. (Obviously from the moment of waking, A and B will start forming different memories.) The question is which, if either, of the two resulting people is me? A, B, or neither?

What we definitely can’t do is claim that they are both me. If this were true, then A and B would also be identical to one another: If A = C and B = C then A = B. But this logically cannot be the case, since A and B are not identical. A and B will go on to lead different lives; one could get a brain disease, the other not, and so on. However, it is logically possible that I am A, B or neither. But how could we decide which option is true?

To illustrate that in fact we cannot decide between these options, Swinburne asks us to further imagine that before the brain split and transplant operation the surgeon tells me his rather macabre plan: one of the resultant clone/original fusions will be given a fortune, and the other will be subject to torture. I am asked to decide which one will suffer which fate. It seems I am faced with an impossible task: which fusion person should I choose for which fate, assuming that I would choose me to have the money? There is no logical contradiction in claiming that I survive as A, as B, or as neither. But if, as we stated, they have equivalent physical continuity with me, and mostly identical characters and memories, yet knowing all this we nevertheless still haven’t been given sufficient information to decide which is me (if either), what then is it that makes me ‘me’? We have stipulated physical continuity, and continuity of memory and character: the point is that these properties are not sufficient to determine the continuity of identity. And yet the continuity of identity is nevertheless a logical possibility: it is still logically possible that only one of the new entities is me.

If one accepts this conclusion that the continued existence of the self is logical possible independent of our knowledge of the continued existence of brain matter, memory or character, can we say anything about metaphysical possibility here? As argued earlier, a logical possibility becomes a metaphysical possibility if informative designators can pick out the substances involved. Swinburne next argues that ‘I’ is an informative designator: when all our faculties are working and we’re not subject to illusion, I cannot be mistaken about when to apply the designator ‘I’. I cannot reasonably look in the mirror and not recognise that it would be appropriate to use the term ‘me’ or ‘I’, for instance. Or I cannot be mistaken about the usage of the word ‘I’ when I say ‘I am in pain’. Given that ‘I’ is an informative designator, and since it is logically possible that I survive independent of retaining my matter, character or memories, it follows that it is also metaphysically possible that I survive independent of retaining my matter, character or memories. (Or that I don’t.)

The Implications

To see the implications of this conclusion requires the introduction of a final theory: the principle of the Identity of Composites. This principle states that anything made of the same parts with the same history arranged in the same way has to be that exact thing in any possible world. This is a logical necessity. Take a car, for example. We cannot conceive of a universe where there is a car made of all the same parts, with the same history as a car in our universe, without it being the same car.

Now we have already stated that in our brain-splitting thought experiment it is metaphysically possible that one of the clone/original fusions – say, A – is me, and that it is also metaphysically possible that A is not me. But if A is in fact me, then given the principle of the Identity of Composites there cannot be any metaphysical possibility of A not being me, if A only consists of the same physical parts, with the same physical properties arranged in the same way (and perhaps associated mental properties too). So either our conclusions are wrong, or what constitutes ‘me’ cannot be reduced to the physical parts and their associated mental properties. Given the principle of the Identity of Composites, and also given that my surviving and not surviving the operation are both metaphysical possibilities, there must therefore be something that is me independent of having the same physical parts with the same properties. Otherwise only one of these options – either A is me, and must be me, or A is not me and cannot be me – is metaphysically possible. Otherwise we are claiming that the same physical parts arranged in the same way have the possibility of being different substances – that A is at the same time possibly not A – contradicting the principle of the Identity of Composites. However, if what makes me me is a non-physical thing, then we can retain our assumption that the clone/original fusion has the metaphysical possibility both of being me or not being me, as the fusion being may or may not include an extra non-physical component!

At this point an objection can be raised – one that Swinburne pre-empts. In our thought experiment, the original person C shares brain matter with each of the resulting clone/original fusions A and B. So perhaps it could be argued that for a new person to be me it is metaphysically necessary for at least some of my brain to be present in the new person. To counter this possibility Swinburne invents another thought experiment to show that continuity of brain matter, as well as of memory or character, does not determine whether I survive over time.

Imagine that someone has a brain disease, and has to have part of their brain replaced with compatible organic matter; let us say 10% of their brain. Now let us say that the disease spreads, and they have to have another 10% of their brain replaced; and another 10%… until the entire brain matter has been replaced. It is logically (and, as has been shown by previous arguments, metaphysically) possible both that the resulting person is X, and that it is not X. Clearly, one of these alternatives will be true (the person either will or won’t be X), but the point is that the truth is not entailed by any continuity of brain matter, nor anything about how much memory or character is shared between the person at the start and at the end of the series of operations.


In both our thought experiments, we have shown that continuity of matter, memory or character are not sufficient to constitute identity. The critic could still argue that one or more of these are necessary conditions for identity; after all, in both cases some sort of continuity is present. But how do you define the conditions for continuity? How do you place a percentage on how much memory is necessary? If you say 50% memory is enough for personal continuity, then an entity with 49.99% of my memories is not me, and this seems rather problematic. However, an answer would be needed to give a definitive solution to whether or not I survive the above brain experiments.

Perhaps we could opt for degrees of continuity, as in the second experiment, so long as the change in brain matter is gradual. But we still have a similar problem: 10% change and identity is maintained, but 99% change and identity is lost (perhaps) – but where between these two amounts do we settle on the necessary conditions for continuity of identity? It is becoming less and less likely (although admittedly not proven) that there are any necessary conditions for personal identity of the kind described in a complex theory of identity. That no such conditions are necessary is again suggested by the type of sci-fi story where a person acquires a new body without gradual change, a new personality and new memories, yet survives – showing the logical (and so metaphysical) possibility of survival without any such continuities.

The two thought experiments demonstrate that no constituents mentioned in the complex theory, involving continuity either of memory or of brain parts, are sufficient to determine identity, and the necessary conditions for complex identity are less and less likely to be pinned down. Conversely, the simple theory of identity, namely that each person has a ‘thisness’ which is non-physical and which makes it possible for them to survive (or not survive) such brain operations, gains strength.

To summarise, it is both logically and metaphysically possible that I survive an operation in which two entities are created who have continuity with my brain matter, memory and character. This dual possibility is itself only possible if what constitutes ‘me’ is something other than my brain matter, memory or character. This means that the simple version of personal identity is vindicated, and the ‘thisness’ that makes me me is something non-physical. If this were not true, we would not be left floundering as to whether or not I survive the dual brain transplant to be rewarded or tortured. This ‘thisness’ we may call a ‘soul’ – a term many philosophers will be loath to use, but which concept the argument demonstrates deserves at least some consideration. We would then be left with the idea that each embodied human consists of two parts – a body (non-essential to the person’s identity) and a soul (essential to it).

At this point, I will unashamedly avoid the issue of what a soul is, the implications this idea presents, and how it relates to the body. More of that another time, perhaps.

© Sally Latham 2014

Sally Latham is a Philosophy and Anthropology lecturer at Birmingham Metropolitan College. She would like to thank Richard Swinburne for his guidance and patience.

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