Descartes' Substance Dualism

Descartes: Humans are made up of two substances: res extensa/res cognitas

Res extensa: Having extension (taking up space); body has extension

Res cognitas: Lacking extension (not taking up space); mind doesn't have extension

P1: Body is divisible because it's extended - losing a limb doesn't change them as a person; mind is indivisible because it can't be extended - one cannot have half a thought or emotion

P2: Res extensa and res cognita have different properties

P3: If they have different properties, they must be made of separate substances

C: The mind and body are separate otherwise they'd have the same properties

(Uses Leibniz's identity of indiscernibles: things are only identical if they share exactly the same properties)

1) can some bodies never be divided?

• Potential for structure of bodies to be divided further and further, no limit has yet been found - Descartes makes an empirical claim he can't make
• if possibility of indivisible body, then body could be made of same substance as indivisible mind, therefore following Leibniz's law, they are the same thing therefore monoist view of body and mind

2) can some minds be divided into parts?

• potential for divisible mind i.e Phineas Cage, DID
• Jaynes: awareness of one's own thoughts is a recent development, previously thoughts were thought to be commands from a distant deity (potentially religious visions could have interpreted their own thoughts as deity's commands), the mind considered to be bicameral so mind could have two parts
• different functions of the mind could be different parts
  RESPONSE
• parts of the mind have different functions but it is "one and the same" mind that does it

P1 - if one can clearl think of one substance apart from another, they must be different substances
P2 - the mind thinks but isn't extended
P3 - the body is extended and doesn't think
P4 - it is possible to think of a mind without a body
P5 - it is possible to think of a body without a mind
C - the mind and body therefore must be distinct things

1) mind without body is not conceivable

• mental states affect behaviour and bodies are required to show mental states (behavioural psychology: understanding the mind requires close attention to observable behaviour)

2) what is conceivable may not be possible

• possible to conceive Descartes to think of two things as distinct when it's impossible for them to be separated
  RESPONSE
• Descartes: things are only separate if clear and distinct (those which have properties to shared with other things) therefore counter-argument is pointless bc the standard of clarity + distinctness is what ensure the conceivable = possible

3) what is logically possible tells us nothing about reality

• just bc something is logically possible doesn't always mean that is what the world is like
• Descartes needs to demonstrate that is is logically impossible for one substance to be both thinking + extended

• if the mind is non-extended + immaterial and the body is extended + material, how do they interact?

P1 - bodies interact with another by exerting force

P2 - force requires extension

P3 - if the mind is unextended, then it cannot exert force

P4 - if dualism is true, mind is unextended and cannot exert force

P5 - mind can exert force on bodies

C - dualism is false

RESPONSE

• Descartes: there must be some third substance uniting the mind and body
• Descartes: mental causation is different from physical causation so may function differently

1) interaction from non-physical mind requires energy added to universe

• this is impossible following current laws of physics
  RESPONSE
• physics msut be wrong; law of conservation of energy must be wrong; universe can't be a closed system; non-physical substance that creates additional energy

2) changes in brain without physical cause

• changes in brain cause changes in body so non-physical mind would have to cause physical changes, highly unlikely
  RESPONSE
• we might not ever be able to rule that out

1) solipsism (position which holds one can only ever know contents of own mind)

• dualist position means it is possible for bodies without minds to exist
• all we could ever know about other minds is that bodies exist and potentially one could be the only mind in the world
  CRITICISM
• if essential privacy of experience is proven false, solipsism is foundationless
• to appeal to logical rules + empirical evidence, solipsism has to implicitly affirm what it believes in: reality of intersubjectively valid criteria + public/extra-mental world
• requires language (sign system) to affirm solipstic thoughts/language as private bc no other minds (private language arguments) but language is irreducibly public - to doubt/question is to utilise language in publicly accessible way
• non-linguistic solipsism is unthinkable + thinkable solipsism is necessarily linguistic ∴ it presupposes the thing it seeks to deny

2) Mill's argument from analogy
P1 - I have a mind
P2 - I know from experience that my mental states cause my behaviour
P3 - other people have bodies similar to mine + behaviour similarly to me in similar situations
P4 - ∴ by analogy, their behaviour has same type of cause as my behaviour i.e mental statements
C - ∴ other people have minds
CRITICISM

• induction leads to generalisation + possibility of other minds
  RESPONSE
• reframing argument as an inference to the best explanation (abductive)
  P1 - behaviour A has a mental cause (making a noise caused by pain)
  P2 - behaviour B has a mean cause (smiling caused by happiness) and so on
  P3 - many behaviours have mental causes (something one has experienced)
  P4 - I have seen other people exhibit the same types of behaviour
  P5 - these behaviours must also have mental causes
  C - other minds must exist to cause these mental causes

CRITICISM

• Hume: inductive arguments from analogy aren't 100% accurate bc there's a chance such a thing doesn't happen in the future
• possibility others' brain states caused by other things
  RESPONSE
• not analogy bc P1 is type of behaviour, we're simply generalising to causal inference to best explanation - not proving but justifying

CRITICISM

• can we really consider a belief in other minds to be like a scientific hypothesis? Are we justified in taking othe rpeople's behaviours as evidence?

• we learn mental states from other people i.e children don't understand anger until observing others' being angry (attributing to other people)
• implies:
  1) problem of other minds doesn't arise bc no knowledge of oneself as mind without presupposition of other minds existing
  2) knowledge of other minds not inferred from knowledge of own behaviour + its cause (requires both)

CRITICISM
3) substance dualism claims mental properties in minds + physical properties in bodies ∴ how do we identify other minds so as to attribute mental properties to them? No experience of other minds on their own so must be attributed to something with physical properties ∴ both mental + physical properties have to be attributed to same thing ∴ blurring distinction
4) we don't know what a mind is unless we know what a person is (embodied mind) ∴ we can only understand idea of mind by abstracting from idea of person (mind=disembodied person) ∴ concept of union of mind + body is more basic than concept of mind