- Descartes developed an argument known as the "Cogito" to show that he is a thinking thing.
- The intent of this argument was so that he could provide a foundation from which all his philosophy could follow.
- He wanted to create a starting point which was indubitable; an unassailable proposition.
- He could doubt that he had a body, because it was possible to imagine exisiting without one.
- He could doubt the evidence of his senses; a stick in water appears to be bent, but it is not. The brain can suffer from hallucinations and illusions.
- The one thing he could not doubt was that he was a thinking thing; to doubt is to think. Hence the phrase Cogito Ergo Sum (I think therefore I am).
- The body is divisible into parts; arms, legs, organs etc. But the soul is not- it is intangeable. You cannot cut through a soul, therefore it is indivisible.
- The body is physical and perishable, so the soul must be metaphysical and imperishable.
- This lead Descartes to the conclusion that Body and Soul are distinct (separate) in reality.
- But how do a metaphysical soul and a physical body interact with one another? According to Descartes this is achieved through the Pineal Gland, of which we now know is involved in the regulation of sleep.
The Physical Brain and Body:
- Are material substance
- material substance has the property of being extended in space; its esscence is to have size, shape, location and movement
- Material substance can decay, so the body and brain die and decay
- Physical events, including those of the body, are public an observable- anybody can see what you are doing.
- Is soul substance
- Soul substance has property of consciousness / self awareness: the whole esscence of the mind/soul is to think- Soul substance has no extension in space
- Soul substance cannot therefore decay or die., so is immortal
- Mental events are private and unobservable.
From the list above it becomes apparent that the separate qualities of the body and soul suggest that our bodies can undergo radical change without our Personal Identites being affected. Descartes believes that the idea of living on without a body is a conceivable one. The qualities of the mind/soul means that we can survive death yet still exist without bodies and remain "same person".
- Perhaps it is possible to live without an arm and a leg for example, and medical science has shown that in the event of an accident whereby one hemisphere of the brain has to be removed, the remaining hemisphere adopts the functions of the missing part. However, can we really be sure that we would be able to exist without a whole brain?
- If a soul substance is entirely non-physical and the body physical- made of matter- how do the two interrelate? Even if the pineal gland thesis were true, it still does not tell us how the non-physical can possibly interact with the physical, Even Descartes eventually admitted the problem was unsolvable.
- Putting this another way- how can a non-physical mind cause events in the pysical world? How does my thoughts on playing a game of tennis cause the physical outcome of me actually playing tennis?
- Hume raised the problem of counting souls; if the soul has no extension in space, how to we know that there is a ratio of one soul to one body? what is there to stop many minds inhabiting one body? He might also doubt the existence of souls altogether. A soul is an example of irreducable complexity. Hume believes that unless you can track something back to its simple ideas, then the concept is completely meaningless. A soul is an example of a complex idea that cannot be reduced to simple ideas. Therefore, Hume would say it was completely meaningless.
- Furthermore, there is no experimental evidence for the soul. As we just said, the soul is by definition unobservable; brain scans reveal no additional evidence. So isn't it easier to say there isn't one?
- If the mind isn't physical, then why do drugs and alchohol affect it?
- See also Ryle and Behaviourism.