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Ignacio asked:

What is the purpose of the soul in our body? — if it happens to exist?

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I like this way of approaching the mind-body problem. We all-too easily assume that we just know
what difference it would make whether we have a soul, a substantial, non-physical self or not. But do
we know this? So what if I don't have a soul? or so what if I do? What difference doesit make?

Consider the following thought experiment. A mischievous demon has been watching me as I write
these words. Thousands of miles away, across the Atlantic, Ignacio wonders, as he sips his breakfast
coffee, whether the question he has submitted to Ask a Philosopher will be answered this week. Then
the mischievous demon decides to play a nasty trick. The demon takes Geoffrey's soul and places it
in Ignacio's body, and at the same time takes Ignacio's soul and places it in Geoffrey's body.
However, at the moment when Ignacio and Geoffrey's souls are swapped over, all the memories in
Ignacio's soul are erased and replaced with Geoffrey's memories, and all the memories in Geoffrey's
soul are erased and replaced with Ignacio's memories.

'Geoffrey' continues to write his answer to Ignacio, 'Ignacio' continues to sip his coffee. Neither is
aware that anything has happened. — The philosopher who first conceived this thought experiment
was John Locke, in the section on 'Personal Identity', in his book, An Essay Concerning Human
Understanding(1690). Locke imagined the soul of a prince and a pauper swapped while they lay
asleep. But it should be obvious that it makes no difference whether the victims of the prank are
awake or asleep at the time.

But hasanything happened, in reality? Before we can say that anything has happened, whether
Geoffrey or Ignacio are aware of it or not, we need to produce some definition of a 'soul' other than,
'the bearer of memories and the sense of self'. Furthermore, the definition must not be purely
negative, such as, 'the part of the person that is non-physical'. Until such a definition can be
produced, we do not know whether we meananything at all when we talk about 'the soul', or whether,
on the contrary, we are just uttering meaningless sounds.

Here is another thought experiment. While the soul of Geoffrey continues to think about the answer
he is writing, and the soul of Ignacio continues to enjoy the taste of the coffee he is sipping, a second
soul of Geoffrey is thinking exactly similar thoughts and feeling exactly similar feelings as the first soul
of Geoffrey, while a second soul of Ignacio is feeling exactly similar feelings and thinking exactly
similar thoughts as the first soul of Ignacio. But why stop at two? Perhaps Geoffrey and Ignacio each
have a dozen souls, or hundreds of souls, or millions.

Or, on second thoughts, for all you or I know, every second that passes, Geoffrey's soul is
annihilated, and replaced with an exactly similar soul. Every second that passes, Ignacio's soul is
annihilated, and replaced with an exactly similar soul. — These thought experiments were first
conceived by the philosopher Immanuel Kant in the section on the 'Paralogisms of Transcendental
Psychology' in his book, Critique of Pure Reason(1781).

As in the case of the imagined case of Geoffrey and Ignacio's soul-swap, the question is not simply
whether we can knowwhether or not you and I each have hundreds of souls, or an endless
succession of souls, but whether in fact in talking this way any coherent thought has been expressed.
To accept that the concept of a soul has no useful purpose, when seen in these terms, is to admit that
we don't know what we are talking about when we talk about 'the soul'. It is to admit that when we
speak those words, we might as well be uttering meaningless sounds. — That is the challenge posed
by these thought experiments.

Geoffrey Klempner