Learning objective:
To understand Descartes’ divisibility argument;
To evaluate its success.
Substance
Property
divisibility
You need
• Extract from Descartes med VI (conceivability
arg) page 32
• Take in homework – 5 mark question on
conceivability argument
Recap – discuss with a partner
• What is substance dualism?
• What is a property?
• Outline the conceivability argument
• outline the issues –
What is conceivable may not be possible (masked
man)
What is logically possible tells us nothing about
reality
Mind without body is not conceivable (behaviour)
The divisibility argument
• List 5 properties the body has
• List 5 properties the mind has
• Compare your lists – how different are the properties?
• Read page 33 of Meditation VI – what is Descartes’ divisibility
argument?
Descartes claims they have different properties (thought and
extension) If they were the same thing, they would have different
ones.
The body (physical substance) is divisible into parts but the mind
(mental substance) is not, so they must be two types of thing.
(Leibniz – if two things are identical then they share all their
properties. If two things have different properties they cannot be one
and the same thing.)
How successful is Descartes’ divisibility
argument?
1. The mental is divisible in some sense
2. Not everything thought of as physical is
divisible
3. Am I a substance?
1. The mental is divisible in some
sense
Cases of split personalities or mental illness could suggest the mind
can be divided. Or people may believe something consciously and a
different thing unconsciously. Perhaps then we can have ‘parts’ of the
mind.
How would Descartes respond?
• He might say the way the mind is divisible is different – bodies are
spatially divisible but minds only functionally so. Different bits of
the mind might do different things but they are not in separate
locations. So, his argument is still valid.
Furthermore, the argument assumes minds are substances. If they are
not then we cannot talk about their properties. They cannot be
divisible because they are not things! This argument depends on the
conceivability argument to first establish the mind is a substance.
2. Not everything thought of as
physical is divisible
• Physical things have the property of extension
and so are divisible. But is this right? (atoms,
waves, force fields…)
• One could reply that we can still conceive of
them being half the size – there is no logical
limit.
3. Am I a substance?
• Descartes claims he is a thinking thing. He
remains the same from one thought to another.
But is this right? A thinker may just exist for each
thought without persisting from one thought to
another.
• And to be a substance, he must be the same even
when not thinking (e.g. when sleeping
dreamlessly). Can he show this?
Discuss - Do thoughts require a thinker?
Are thinkers substances?
Is the divisibility argument for
substance dualism persuasive?
No
Yes
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Key points on substance dualism
Can you summarise it in less than 5 bullet
points?
Minds and bodies are two distinct substances
They are ontologically independent
Descartes says God can create anything that
he, Descartes, has a cdp of. He has a cdp of
mind and body being separate and so as it is
conceivable it is possible.
Descartes also argues that bodies are divisible
but minds are not so they must be separate
substances.
Homework
• Make notes on the divisibility argument and
the 3 issues we have looked at today.
Lacewing page 207- 210
• Make sure that you can outline both of
Descartes arguments for SD and assess the 3
objections for each.