Am I my body?

By Socrates

I am most fortunate, for I have many friends with whom I enjoy dialoguing. Recently I met Emma. My friend, Paul, introduced us and I now count her among my friends. Earlier today she and Paul invited me for coffee. As often happens, the topic of our talk moved towards an ultimate question, in this case: am I my body?

By the gods, this is a worthy question indeed. But it is not so easy to answer. Our dialogue was recorded and I will soon post the transcript here. In the meantime, good reader, I shall summarize our dialogue.

Emma opened our discussion by asking some questions about the endurance of selfhood over time. She observed that she feels like the same person as she did yesterday, and that yesterday she felt like the same person as the day before. In fact, she said that she thinks she is the same person as she was a year ago, albeit with the addition of new memories. I suggested that she was inferring a continuity of self.

Then things became interesting. Emma told me that all the cells in her body have changed during the past year. Many have died and been replaced by new cells, and at a lower level, the particles that comprise her cells have swapped with other particles. This is part of a science you moderns call quantum physics. This is a science of which I have no wisdom — so I will provisionally accept her word. Emma’s point is that her entire body is made out of different particles than it was a year ago. But because she feels like the same person, at least one part of her has endured. She is not completely distinct from the person she was last year.

We formulated this argument:

P1. (premise) If two objects share none of their properties, they are completely distinct

P2. (premise) I am not an object that is completely distinct from the object I was last year

C1. (conclusion) Therefore, at least one property in me is the same as last year (from P1, P2)

P3. (premise) All my physical properties have changed over the year (the subatomic particles have all swapped with new particles)

C2. (conclusion) Therefore, I must have at least one non-physical property (from C1, P3)

Here we seem to have stumbled upon an argument for a non-physical component of a person. Is this an argument for the existence of a soul? By Zeus, it would be remarkable if this argument went unchallenged. Indeed, it was challenged by our dear friend, Paul, who was not convinced of the truth of our third premise.

Paul constructed an argument designed to refute premise three. He suggested that since our sense of self is encoded in the brain, and the encoding has not changed, premise three is false. Not all physical properties of a person change over time.

Allow me to present his argument:

P1. (premise) My thoughts about whether a soul exists are a characteristic of me

P2. (premise) An attribute, quality, or characteristic of something is a property of that thing

C1. (conclusion) Therefore, my thoughts about whether a soul exists are properties of me (from P1, P2)

P3. (premise) I have had my thoughts about whether a soul exists for more than a year

C2. (conclusion) Therefore, I have had at least one property for over a year (from C1, P3)

P4. (premise) If two objects share none of their properties, they are completely distinct

C3. (conclusion) Therefore, I am not completely distinct from the object I was last year (from C2, P4)

P5. (premise) My brain is what creates/encodes my thoughts about whether a soul exists

C4. (conclusion) Therefore, my thoughts about whether a soul exists are properties of my brain (from P5)

P6. (premise) My brain is a physical object

C5. (conclusion) Therefore, my thoughts about whether a soul exists are physical properties of my brain (from C4, P6)

C6. (conclusion) Therefore, not all my physical properties have changed over the year (from C3,C6)

A wonderful argument from an admirable person. However, an initial examination of the argument revealed a logical error in the move from C2 and P4 to C3. Paul had inadvertently committed the fallacy of denying the antecedent. Here I shall illustrate by rewording the inference.

P1. If two objects share none of their properties, then they are completely distinct

P2. These two objects (i.e the object I was last year and the object I am now) share at least one property

C. Therefore, these two objects (i.e. the object I was last year and the object I am now) are not completely distinct.

The logical error can be seen more clearly with this analogous argument:

P1. If I live in Washington DC, then I live in the United States

P2. I do not live in Washington DC

C. Therefore, I do not live in the United States

This is a faulty inference because it does not follow from P1 and P2 that I do not live in the United States. I may live in New York.

We discussed the problem and it emerged that what he really meant is that to be completely distinct, two objects must share none of their properties. So we included the rewording in his argument:

P1. (premise) My thoughts about whether a soul exists are a characteristic of me

P2. (premise) An attribute, quality, or characteristic of something is a property of that thing

C1. (conclusion) Therefore, my thoughts about whether a soul exists are properties of me (from P1, P2)

P3. (premise) I have had my thoughts about whether a soul exists for more than a year

C2. (conclusion) Therefore, I have had at least one property for over a year (from C1, P3)

P4. (premise) To be completely distinct, two objects must share none of their properties

C3. (conclusion) Therefore, I am not completely distinct from the object I was last year (from C2, P4)

P5. (premise) My brain is what creates/encodes my thoughts about whether a soul exists

C4. (conclusion) Therefore, my thoughts about whether a soul exists are properties of my brain (from P5)

P6. (premise) My brain is a physical object

C5. (conclusion) Therefore, my thoughts about whether a soul exists are physical properties of my brain (from C4, P6)

C6. (conclusion) Therefore, not all my physical properties have changed over the year (from C3,C6)

After some dialogue, we found that Paul had made an assumption that could be challenged. His assumption is that the physical encoding of a thought is identical to the thought itself. By questioning whether it would be possible to encode a thought in two distinct physical systems, I revealed a weakness in that assumption.

So we moved on to construct a third argument in response to Paul’s.

P1. (premise) I have an idea of X

P2. (premise) The instance of my idea of X is encoded in neurons

P3. (premise) Last year my idea of X was encoded in different neurons (due to quantum particle swapping)

C1. (conclusion) Therefore, the two instances of my idea of X are not identical with each other (from P1, P2, P3)

P4. (premise) The content of my idea of X is the same as last year

C2. (conclusion) Therefore, the content of my idea of X is something other than the encoded instances of X (from C1, P4)

P5. (premise) If the content of my idea of X is something other than the encoded instances of X, then the content of my idea of X is not a physical property of my brain

P6. (premise) The content of my idea of X is “whether or not a soul exists”

P7. (premise) We call the content of my idea of X “my thoughts about X”

C3. (conclusion) Therefore, my thoughts about whether or not a soul exists are not physical properties of my brain (from C2, P5, P6, P7)

It appears that we have again deduced that thoughts are not physical properties of the brain. At this point we decided to break from the discussion as Emma had to return to work. There is, after all, only so much progress to be made during a lunch break.

Our dialogue produced some worthy arguments. I strongly suspect that I will be invited to continue the discussion with these remarkable people at another time. There is still much work to be done.

— Socrates

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