1. Scepticism: Descartes’ 3 waves of doubt illusion, deception, dreaming & Putnam’s Brain in a Vat

2. 1st wave: Illusion
Descartes begins his method of doubt by considering that in the past he has been deceived by his senses:
Things in the distance looked small; sticks in water appeared bent
However, Descartes finally accepts that these could be perceptual illusions (as they are special cases)

3. Conclusion
The occurrence of perceptual illusions are not commonplace enough to make us doubt our everyday knowledge
There, the first wave of doubt isn’t enough to knock our knowledge off its feet
We can continue to trust that most of our everyday perceptions accurately reflect the way the world is

4. But clearly, either way, I am a very handsome man
2nd wave: Dreaming
‘There are no conclusive signs of which one can distinguish clearly between being awake and being asleep’
But clearly, either way, I am a very handsome man

5. Scepticism and dreaming
Descartes’ 2nd wave of doubt argues that we could be dreaming; this attacks all sense-perception, even the most mundane and the most certain
E.g. You cannot know that you are sitting on a chair because you cannot know you are not dreaming of sitting on a chair
Go on…try and prove you’re not dreaming it.

6. Vanilla Sky
In the Tom Cruise film Vanilla Sky, the main character moves between two different periods of time throughout the film
The audience is aware that something is not coherent about his life
In the end, he discovers he has been dreaming
The audience realises only the first 20 minutes really happened
…but it seemed real to me at the time. How do you know you weren’t dreaming your whole life either?

7. Replies to dreaming
Some philosophers have responded by saying that dreams are much less coherent than reality
I often dream that my mother is a cactus but when I open my eyes, she rarely is

8. Descartes reply
Descartes agrees that some dreams have less coherence than reality
However, this one particular dream could be a perfect imitation of reality
We cannot know that this particular moment is not a moment in a particularly realistic dream

9. Conclusion I cannot prove that I am not dreaming
If I cannot prove that I am not dreaming that I cannot be sure my current sense experiences truly reflect the way the world is
I therefore cannot be sure of any knowledge based on sense experience
However, one thing I can be sure of is the truths of maths and logic…hurrah

10. The 3rd wave: Deception The evil demon
For the sake of argument, Descartes next suggests that all of our experiences are produced by an evil demon who wants to deceive us
The possibility of this being true means that none of my experiences are real
All my beliefs about the external world and events in time are thrown into doubt because it is based on experience (which the evil demon controls)
Even the truths of maths and logic could be lies!

11. How can thoughts be trusted when the evil demon can control them too?
Can I trust my memories, if the evil demon controls the things in my mind?
Can I trust others, if the evil demon controls all of my experiences?
No! You can trust nothing hahahahahahhhahahhahhahhahahhahah(hic!)
Curses…laughing always gives me hiccups

12. Putnam’s brain in a vat theory
Descartes argument from deception appeals to an evil demon
A modern version of that idea is that we are not really walking, talking human beings but simply brains in vats.

13. Putnam’s Brain in a vat theory
Connected to my brain is a super-computer that feeds in just the right impulses to generate the illusion of reality
So I still have sensations of touch, taste, sight etc but they do not reflect any sort of reality
I cannot know that this is not true as things seem exactly the same as if I am a walking, talking human
In this way, neither my senses nor my reasoning can be trusted.
See if you can identify one good reason to believe you are not a brain in a vat…

14. Conclusion Descartes: God would not allow me to be deceived!
My ideas are clear and distinct
God is good and I can therefore trust that what I know clearly and distinctly must be true or God would be allowing me to be deceived
Putnam: I can’t really be a brain in a vat as then I couldn’t really know what a vat is and the whole thing wouldn’t make sense anyway!

15. Can you complete this sentence...
For Plato our senses can/cannot be trusted because…

16. Who was Rene Descartes?

17. Explore Rene Descartes answer to
Today we will...
Explore Rene Descartes answer to
‘What is Reality?’
Understand what Descartes meant by ‘Cogito Ergo Sum’
Explain Descartes Scepticism and Rationalism
Make links between Descartes and Plato

18. The philosophy behind INCEPTION
Rene Descartes pondered the same questions as the film INCEPTION makes us think about. Descartes argued that because we can not know whether or not we are dreaming… He wanted to know what it is possible to know beyond doubt!

19. Scepticism
He tried to doubt everything, even those things that appeared obvious!
His aim was to find things we can be 100% certain of
Descartes noted that senses sometimes deceived us

21. INCEPTION…
… is about a thief who possesses the power to enter into the dreams of others. Dom Cobb (Leonardo DiCaprio) doesn't steal things, he steals ideas. By projecting himself deep into the dreams of his targets, he can steal information.

22. Watch this clip… (4.22 mins long)
The philosophy behind inception…
Watch this clip… (4.22 mins long)
“Dreams feel real whilst we are in them. It is only when we wake up that we realise something was actually strange” Cobb
Can Cobb possibly know whether or not he is dreaming?

23. “Cogito ergo sum”

24. Descartes concluded that there was only one thing he could be sure of...
THINK!
If we doubt and question the existence of everything in this classroom What is the ONE thing you would be most sure of and why?

25. What do you think this means?
“I think, I am”
What do you think this means?

26. He found an unshakeable truth that no doubt could assail.
HE EXISTED, since it was he that doubted

27. True knowledge exists beyond this world Some things are beyond doubt
Do you agree?
True knowledge exists beyond this world
Just because an argument is logical it does not mean it is actually true
Some things are beyond doubt
Thinking is not as a good as evidence
Fact is more important than thinking
I can know things other than myself

28. Reason rather than experience is the basis of all our knowledge
Rationalism
Reason rather than experience is the basis of all our knowledge
Why would we describe Descartes as a rationalist?

29. Why is he such an influential thinker?
Is our logic and our thinking a challenge to everyday evidence that we get from our senses?
Why would we see pictures of Descartes in the maths, science and PRE corridors?
Why is he such an influential thinker?