1. Descartes’ divisibility argument
Learning objective:
To understand Descartes’ divisibility argument;
To evaluate its success.
Key Words
Substance
Property
divisibility

2. You need
Extract from Descartes med VI (conceivability arg) page 32
Take in homework – 5 mark question on conceivability argument

3. 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)

4. 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.)

5. How successful is Descartes’ divisibility argument?
The mental is divisible in some sense
Not everything thought of as physical is divisible
Am I a substance?
Spend time looking at the 3 issues and discussing them

6. 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.

7. 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.

8. 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?

9. Is the divisibility argument for substance dualism persuasive?No
Yes
Post its

10. 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.

11. Homework
Make notes on the divisibility argument and the 3 issues we have looked at today. Lacewing page
Make sure that you can outline both of Descartes arguments for SD and assess the 3 objections for each.