QuestionsWho am I, really?I can know everything about my brain without knowing whether I survive: so I am more than my brain
Who am I, really?A soul

I can know everything about my brain without knowing whether I survive: so I am more than my brain

The divided-brain argument

Richard Swinburne born 1934God's existence is the simplest explanation of the universe, its order and consciousness.
See profile
What it claims

There is more to me than the matter of my body and brain: an essential, non-physical part, which Swinburne calls the soul, and whose continuation makes this brain and body mine.

Why

If a brain is cut in two and each half is transplanted, we know all about the matter but not which of the two survivors will be me.

The same idea through history
René Descartes1641Descartes concludes that I am a thing that thinks, distinct from the body. Swinburne keeps the conclusion but changes the proof: no longer doubt, but the case of a brain that can be divided.Joseph Butler1736Butler argues that consciousness of self already presupposes the identity of the person and so cannot constitute it. Swinburne draws from this that personal identity is a basic fact, which cannot be analysed.Thomas Reid1785Reid objects to Locke that memory does not make identity, with the example of the brave officer. Swinburne extends this line with a modern case, the transplant of a divided brain.
Richard Swinburne1984Swinburne presents the argument in "Personal Identity: The Dualist Theory" (1984), then takes it up again in The Evolution of the Soul (1986) and The Existence of God (2nd ed., 2004). The text quoted here is that of 2004.
In short

"I can know everything about my brain without knowing whether I survive: so I am more than my brain" is an argument by Richard Swinburne (The Existence of God, 2nd ed., ch. 9 (2004); "Personal Identity: The Dualist Theory" (1984), 1984) on the question "Who am I, really?" (answer: a soul). Its claim: There is more to me than the matter of my body and brain: an essential, non-physical part, which Swinburne calls the soul, and whose continuation makes this brain and body mine. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P5). AskPhilosophy presents 3 objections, 1 of them with a documented reply, and the original text behind each premise, checked word for word.

The Existence of God, 2nd ed., ch. 9 (2004); "Personal Identity: The Dualist Theory" (1984)
Valid with an implicit premise

Suppose my brain is cut in two and each half is transplanted into an empty skull, so that there are two living, conscious persons. Swinburne notes that I could know everything that happened to every atom of my brain, and still not know which of these two beings is me: the first, the second, or neither. It would be a real question of fact, not of words: the surgeon who promises a happy life to one and torture to the other leaves me facing a real question. So, he says, there is more to me than matter: an essential, non-physical part, which he calls the soul.

P1Imagine my brain divided into two and each half transplanted into an empty skull, with what is needed for two living, conscious persons to result. Swinburne sees no insuperable theoretical difficulty.
P2The two persons cannot both be me: if both were identical to me, they would be the same person as each other, and they are not. What remains: the right-half person, the left-half person, or neither.
P3Knowing everything that happens to brains, bodies or anything else physical does not tell which of the three cases is the right one. We do not know what happens to persons.
P4It is not a matter of definition: it is a real question of fact. If the surgeon promises one survivor a happy life and the other torture, whether my future life will be happy or painful, or whether I survive, is clearly a question of fact.
P5 · implicit premiseIf a real question of fact about my survival stays open when all the physical facts are known, then there is an essential part of me that is not physical.
Therefore there is more to me than the matter of my body and brain: an essential, non-physical part, which Swinburne calls the soul, and whose continuation makes this brain and body mine.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P5, the computer finds a case where the question stays open and factual, and yet everything is physical: for instance because there is a physical fact we do not yet know, such as a detail of the brain that determines which of the two survivors continues the same person.
The argument is valid with the hidden premise P5. Division of the brain is possible (P1). The two survivors cannot both be me (P2). The physical facts do not say which one is (P3). This question is factual (P4). So, by P5, there is a fact about me that is not physical. Objections target P4 (is this not simply a choice of words?) and P5 (does a non-physical fact have to be a soul?).
Analogy. Imagine two bundles of pages made by cutting a book in two. One can know every word and every page, and yet the question "which half is the book?" is not settled by counting words. Swinburne thinks it is the same with "which half is me?": it concerns something other than the parts.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

Derek Parfit 1984 · attacks premise 4

There is no "further fact" about personal identity, deep and distinct from the physical and psychological facts. Parfit thinks we have sufficient evidence to reject that idea. In the case of division, the question "which one is me?" is empty: knowing everything that happens is enough to know everything.

Swinburne replies
see the argument
Richard Swinburne 2004 · Swinburne, in the same text
Swinburne writes that it is tempting to say that it is a matter of arbitrary definition, but that this temptation must be resisted: there is a real question of fact. He illustrates it with the mad surgeon who promises one half a happy life and the other torture: whether my life will be happy or painful, or whether I survive, is clearly a question of fact.
Derek Parfit 1984
Parfit answers that what matters is not identity but Relation R: psychological connectedness and continuity with the right kind of cause. The surgeon therefore does not ask the question we think: one can know everything about Relation R between me and each survivor, and that is what matters for my future.
The debate goes on (our summary) Our summary: Parfit (Reasons and Persons) and Swinburne (Personal Identity) were published in the same year, 1984. The Swinburne passage cited above comes from his 2004 version: it answers the general objection "it is a matter of words", not Parfit himself.
Where the debate stands (our summary)Our summary: a basic disagreement. For Swinburne, the question "what happens to me?" always has a true or false answer. For Parfit, it does not, and what matters can be measured without it.
David Lewis 1976 · attacks premise 2

In the case of division, one can say that, before the operation, there were already two persons sharing the same body and the same mental life, up to the operation. After the division, each goes on alone. The two survivors are then two persons who already existed. So there is no unanswerable question "which one is me?"

no reply
We have not yet found a direct reply by Swinburne in the texts.
The debate goes on (our summary) Our summary: Swinburne's answer to Lewis was not found in our sources. The difficulty with Lewis's idea is how to count persons before the operation: we usually count only one.
Where the debate stands (our summary)Our summary: an open point. Philosophers who accept counting two persons before the division avoid Swinburne's argument, but at the price of a counter-intuitive idea.
Sydney Shoemaker 1984 · attacks premise 5

In the same volume, Shoemaker defends a materialist view: personal identity rests on a psychological continuity realized in the brain, with no soul. There is no need to suppose a non-physical fact to explain what happens to persons in transplant cases.

no reply
see the argument
We have not yet found a direct reply by Swinburne in the texts.
The debate goes on (our summary) Our summary: the two authors wrote a book together in which each defends his thesis. We did not re-read any direct exchange between them (book under copyright), so we do not report any.
Where the debate stands (our summary)Our summary: an open point. The divided-brain case is a test that both camps claim to have passed.