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Desartes, Philosophy
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Descartes on DualismDescartes on DualismStephen LawStephen Law
Descartes on dualismDescartes on dualism
Descartes is of course a dualist. But what is dualism?
Students often muff this. They say something like “Dualism is the view that mind and body are different”.
In fact the key term to use here is substance. A “substance” is something that is not dependent upon any other thing for its existence.
Descartes is of course a dualist. But what is dualism?
Students often muff this. They say something like “Dualism is the view that mind and body are different”.
In fact the key term to use here is substance. A “substance” is something that is not dependent upon any other thing for its existence.
Distinct substancesDistinct substances Being substances means each can
exist on its own, without the other. So substance dualism entails that minds can exist on their own: disembodied.
Being substances means each can exist on its own, without the other. So substance dualism entails that minds can exist on their own: disembodied.
Oh! my mind has floated off from
my body!
Body
Mind
An Argument for DualismAn Argument for Dualism
Descartes is often portrayed as offering an argument for Dualism called the THE ARGUMENT FROM DOUBT.
Here’s a first example of such an argument…
Descartes is often portrayed as offering an argument for Dualism called the THE ARGUMENT FROM DOUBT.
Here’s a first example of such an argument…
FIRST ARGUMENT FROM DOUBT I don’t doubt I exist I do doubt my body exists Therefore, I am not identical with my
body This argument is an application of
Leibniz’s law: If objects are identical, they share all
the same properties (so, if they don’t share all the same properties, they are not identical).
FIRST ARGUMENT FROM DOUBT I don’t doubt I exist I do doubt my body exists Therefore, I am not identical with my
body This argument is an application of
Leibniz’s law: If objects are identical, they share all
the same properties (so, if they don’t share all the same properties, they are not identical).
Leibniz’s LawLeibniz’s Law
We regularly use this law to show that things are not identical. Suppose you are an explorer and you discover a mountain…
We regularly use this law to show that things are not identical. Suppose you are an explorer and you discover a mountain…
Leibniz’s lawLeibniz’s law
Later you discover another mountain. Only you are not sure if it is a new mountain. Maybe it’s just the first mountain seen from a different angle? How might you show that the mountains are not identical?
Later you discover another mountain. Only you are not sure if it is a new mountain. Maybe it’s just the first mountain seen from a different angle? How might you show that the mountains are not identical?
Leibniz’s lawLeibniz’s law Find a property one mountain has but not the
other. For example, if you show that mountain 1 is 10K feet high and mountain 2 is not 10K feet high, you can then apply Leibniz’s law like so: Mountain 1 is 10K feet high Mountain 2 is not 10K feet high Therefore Mountain 1 is not identical with
mountain 2. This argument is COGENT!
Find a property one mountain has but not the other. For example, if you show that mountain 1 is 10K feet high and mountain 2 is not 10K feet high, you can then apply Leibniz’s law like so: Mountain 1 is 10K feet high Mountain 2 is not 10K feet high Therefore Mountain 1 is not identical with
mountain 2. This argument is COGENT!
Leibniz’s lawLeibniz’s law
Our first argument from doubt has the same form.
It points out that I and my body differ in our properties: one has the property of being something I doubt exists whereas the other does not.
The argument concludes that I am not identical with my body.
Our first argument from doubt has the same form.
It points out that I and my body differ in our properties: one has the property of being something I doubt exists whereas the other does not.
The argument concludes that I am not identical with my body.
Refuting the argument from doubt - masked man fallacyRefuting the argument from doubt - masked man fallacy
Suppose I see a masked man robbing a bank.
Suppose I see a masked man robbing a bank.
Masked man fallacy (cont.)Masked man fallacy (cont.) Later, my father is accused. Can I prove
his innocence like so? I don’t doubt the masked man robbed
them bank I do doubt my father robbed the bank Therefore the masked man is not
identical with my father
Later, my father is accused. Can I prove his innocence like so? I don’t doubt the masked man robbed
them bank I do doubt my father robbed the bank Therefore the masked man is not
identical with my father
Masked man fallacy (cont.)Masked man fallacy (cont.) The property of being someone I doubt
robbed the bank is not a property to which Leibniz’s law applies. True, my father has this property and the robber doesn’t. But that doesn’t entail that my father is not the asked man.
Leibniz’s law does not apply to properties involving someone’s attitude towards a thing (liking, hating, believing, hoping, etc.)
The property of being someone I doubt robbed the bank is not a property to which Leibniz’s law applies. True, my father has this property and the robber doesn’t. But that doesn’t entail that my father is not the asked man.
Leibniz’s law does not apply to properties involving someone’s attitude towards a thing (liking, hating, believing, hoping, etc.)
Masked man fallacyMasked man fallacy This argument from doubt also seems to
commit the fallacy: I don’t doubt I exist I doubt my body exists Therefore I am not identical with my body
The property of being something I doubt exists is a property involving my attitude towards something.
This argument from doubt also seems to commit the fallacy: I don’t doubt I exist I doubt my body exists Therefore I am not identical with my body
The property of being something I doubt exists is a property involving my attitude towards something.
A second argument from doubtA second argument from doubt
What about this argument from doubt:
I CANNOT doubt I exist I CAN doubt my body exists Therefore: I am not identical with my
body
Does this argument far better?
What about this argument from doubt:
I CANNOT doubt I exist I CAN doubt my body exists Therefore: I am not identical with my
body
Does this argument far better?
The second argument refutedThe second argument refuted
Define “wibble”: whoever is actually Bert’s favourite person. I CANNOT doubt I am in pain I CAN doubt wibble is in pain Therefore I am not wibble.
But I could still be wibble. So it seems what I can or cannot doubt also isn’t a property to which Leibniz’s law applies.
Define “wibble”: whoever is actually Bert’s favourite person. I CANNOT doubt I am in pain I CAN doubt wibble is in pain Therefore I am not wibble.
But I could still be wibble. So it seems what I can or cannot doubt also isn’t a property to which Leibniz’s law applies.
Two arguments from doubtTwo arguments from doubt I don’t doubt I exist I doubt my body exists Therefore I am not my body
I CANNOT doubt I exist I CAN doubt my body exists Therefore I am not my body
Summary: Neither argument is valid.
I don’t doubt I exist I doubt my body exists Therefore I am not my body
I CANNOT doubt I exist I CAN doubt my body exists Therefore I am not my body
Summary: Neither argument is valid.
Descartes’ divisibility argumentDescartes’ divisibility argument
My mind is indivisible My body (brain) is divisible Therefore: I am not my body (brain)
This is also an application of Leibniz’s law. Is this argument valid? (reminder - valid
means: necessarily: if the premises are true, so is the conclusion).
My mind is indivisible My body (brain) is divisible Therefore: I am not my body (brain)
This is also an application of Leibniz’s law. Is this argument valid? (reminder - valid
means: necessarily: if the premises are true, so is the conclusion).
Descartes’ divisibility argumentDescartes’ divisibility argument
My mind is indivisible My body (brain) is divisible Therefore: I am not my body (brain)
Yes it is valid! But that does not mean it’s a good argument.
What might be wrong with it?
My mind is indivisible My body (brain) is divisible Therefore: I am not my body (brain)
Yes it is valid! But that does not mean it’s a good argument.
What might be wrong with it?
Descartes’ divisibility argumentDescartes’ divisibility argument
My mind is indivisible My body (brain) is divisible Therefore: I am not my body (brain)
The first premise may be question-begging. Your mind might not seem divisible. But if it’s your brain, it is!
My mind is indivisible My body (brain) is divisible Therefore: I am not my body (brain)
The first premise may be question-begging. Your mind might not seem divisible. But if it’s your brain, it is!
Descartes’ divisibility argumentDescartes’ divisibility argument
The Corpus Callosum case.
This illustrates that while we might not think our minds are divisible, they are!
The Corpus Callosum case.
This illustrates that while we might not think our minds are divisible, they are!
Two different failingsTwo different failings
The divisibility argument is VALID but has a dubious premise.
The two arguments from doubt are INVALID (even if their premises are true).
So the arguments all fail, but for different reasons.
The divisibility argument is VALID but has a dubious premise.
The two arguments from doubt are INVALID (even if their premises are true).
So the arguments all fail, but for different reasons.
Descartes’ legacyDescartes’ legacy
Descartes has been profoundly influential. However, examined more closely, his arguments seem fallacious).
That is not to say there aren’t better arguments for dualism.
Cartesian substance dualism is no longer very popular. However, property dualism remains fairly popular among some philosophers (e.g. David Chalmers).
Descartes has been profoundly influential. However, examined more closely, his arguments seem fallacious).
That is not to say there aren’t better arguments for dualism.
Cartesian substance dualism is no longer very popular. However, property dualism remains fairly popular among some philosophers (e.g. David Chalmers).