1. Get Yourself Thinking…
Unscramble the terms we used last week:
DIMN
DBYO
SHYPLACI
TENLAM
LUDAMSI
BODUT
CRTESDASE
TSBUSNAEC
REPOYTPR

2. Get Yourself Thinking…
Unscramble the terms we used last week:
DIMN
DBYO
SHYPLACI
TENLAM
LUDAMSI
BODUT
CRTESDASE
TSBUSNAEC
REPOYTPR
MIND
BODY
PHYSICAL
MENTAL
DUALISM
DOUBT
DESCARTES
SUBSTANCE
PROPERTY

3. What can you remember? Whiteboards! No notes!
Substance Dualism
What can you remember? Whiteboards! No notes!
A substance is something that does not depend or rely on anything else to exist.
A property is something that relies on a substance to exist.
Substance dualism is the view that there are two distinct types of substance in reality – physical and mental.
A major proponent of Substance Dualism was Descartes who believed that we could doubt everything except our existence as a thinking thing. This is known as “Cogito Ergo Sum” or “I think, therefore I am”.
He believed that because we could doubt our bodies (physical) but not our thoughts (mental) it showed that they were two distinct substances (dualism).

4. Argument from divisibility: Argument from conceivability:
Substance Dualism
The Arguments:
Argument from doubt:
My body can be doubted.
I cannot be doubted. (Cogito)
Therefore I am not my body.
NOTE: Descartes denies using this argument and it is never explicitly written in his work.
Argument from divisibility:
I am indivisible.
My body is divisible.
Therefore I am not my body.
Argument from conceivability:
I can conceive of my body as a physical non- thinking substance.
I can conceive of myself as thinking, non- physical substance.
Therefore I am not my body.

5. Quick Detour: Leibniz’s Law
The arguments put forward by Descartes all use a variation of Leibniz’s Law (named after Gottfried Leibniz ):
Leibniz’s Law (also called the Indiscernibility of Identicals): If two things have all the same properties, then they are the same thing (they are identical).
Conversely, If two things do not have the same properties, they are not the same thing (not identical).
This table has 4 legs.
This stool has 3 legs.
Therefore according to Leibniz’s law they are not the same thing.

6. Quick Detour: Leibniz’s Law
Seems obvious but is applied in many different areas in many different ways:
Compare the things in these pictures using Leibniz’s Law…
The Prime Minister…

7. Argument 1 Divisibility Read through the paragraph from Meditation 6.
What argument is Descartes offering here?
Can you put it into premises / conclusion form?
There is a great difference between the mind and the body. Every body is by its nature divisible, but the mind can’t be divided. When I consider the mind — i.e. consider myself purely as a thinking thing—I can’t detect any parts within myself; I understand myself to be something single and complete. The whole mind seems to be united to the whole body, ·but not by a uniting of parts to parts, because: If a foot or arm or any other part of the body is cut off, nothing is thereby taken away from the mind. As for the faculties of willing, of understanding, of sensory perception and so on, these are not parts of the mind, since it is one and the same mind that wills, understands and perceives. They are (I repeat) not parts of the mind, because they are properties or powers of it·. By contrast, any corporeal thing can easily be divided into parts in my thought; and this shows me that it is really divisible. This one argument would be enough to show me that the mind is completely different from the body, even if I did not already know as much from other considerations.

8. What did he think this could show about physical things (i.e. bodies)?
Argument 1
Divisibility:
Think back to Descartes ideas about the body and mind we covered last year. We looked at an example based around a piece of wax.
What did he think this could show about physical things (i.e. bodies)?
He argues that because it is extended in space, body is divisible. But mind, being non-extended, is indivisible. Since mind and body have these different properties, they cannot be the same thing (according to Leibniz’ law).

9. Back to the arguments: Divisibility: I am indivisible.
My body is divisible.
Therefore I am not my body.
“When I consider the mind- ie. consider myself purely as a thinking thing – I can’t detect any parts within myself; I understand myself to be something single and complete.” Descartes

11. Recap Task: Outline Leibniz’s law with an example.
What is Descartes argument from indivisibility?
Can you identify any issues with this argument?

12. Back to the arguments: Divisibility: I am indivisible.
My body is divisible.
Therefore I am not my body.

13. Problems: 1. I am indivisible
Modern neuroscience seems to show this first premise to be flawed, cutting up the brain seems to literally divide the mind (in this case between word and picture functions for example).
There also seems to be some subconscious or unconscious elements to our mental states – there are certain things our minds do that we cannot prevent, automatic thoughts and actions. Some psychotic issues like multiple personality disorder and schizophrenia are also down to the unconscious mind. This seems to be an obvious division.

14. Response: 1. I am indivisible
Descartes does have a potential way of avoiding this critique however, by attempting to show that the mental and physical things are divisible in different ways.
Physical objects are spatially divisible – it can be divided into smaller things that occupy a different space than the original whole. But the mind is functionally divisible- we can divide it into the different functions it performs, but these aren’t performed by physically separate parts which occupy different locations.
So Descartes can still claim that mind is not physical, because the physical is spatially divisible and the mind is not.

15. Can we divide sub-atomic particles?
Problems:
2. My body is divisible.
It may seem obvious that normal physical objects are divisible into different parts (table into board and legs etc.) but there is a genuine scientific question about whether physical substance is infinitely divisible.
Can we divide atoms?
Can we divide sub-atomic particles?
The advancement of modern quantum science presents a very big problem for substance dualists using this argument because there are various theories about what the smallest kinds of substance are. Force fields, waves, or packets of energy have all been suggested. Is a force field spatially divisible? Or a packet of energy?

16. Problems: Overall Problem:
There appears to be physical states that humans (and indeed other things) can be in that are not divisible:
Can being too hot be divided?
Can running be divided?
Does this mean they are part of some indivisible substance? Of course not, it just means the concept of divisibility does not apply to this particular state, perhaps they could be said instead to be properties of a divisible substance.
What if mental states were the same?

17. Back to the arguments: Divisibility: I am indivisible.
My body is divisible.
Therefore I am not my body.

19. Create a Revision Poster:
Outline Leibniz’s law with an example.
What is Descartes argument from indivisibility?
Why might some people argue that mental things can be divided? What examples have we seen? Are there any responses to this criticism?
Why might philosophers argue that physical things cannot be divided? What examples have we seen?
Is there a case for stating that the mind is merely a property of the physical? (Think about other properties that can’t be divided)

20. Something to think about – Am I a substance?:
For my part, when I enter most intimately into what I call myself I always stumble on some particular perception or other, heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never observe anything but the perception - Hume
Hume as an empiricist believed we could only know to be true what we experience. He did not think we experienced “ourselves” as existing things, instead he thought we simply experienced various individual thoughts, emotions, feelings and desires. For Hume this was not enough to show the existence of a thinker just the existence of these individual mental events.
Even if we go as far as stating that each thought, emotion or desire must have a thinker there is nothing to suggest that they all come from the same one, Descartes simply assumes that they must do.
Similarly, if Descartes wants to state that we are only indubitable as long as we are thinking then what about those times at night when we stop thinking consciously? Do we simply drop out of existence? What is keeping us persistent from day to day? For us to be an indubitable substance, we need more than just thoughts.