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1. Michael Lacewing Scepticism Michael Lacewing
enquiries@alevelphilosophy.co.uk
2. What scepticism is Nothing is known
Is this claim itself known?
Our beliefs are all false
Not logically coherent: I am not at the North Pole and I am not at the South Pole cannot both be false at the same time
Challenge: our usual justifications are inadequate
3. Assumptions Reality is logically distinct from appearance
Evidentialism: justification depends on available evidence
Infallibilism: knowledge requires not just that we arent mistaken, but that we couldnt be
4. Perception Perceptual illusions
Illusions depend on veridical perception
Stronger: we only perceive appearances (sense-data)
We cant know what reality outside the mind is like
5. Dreaming Can I know Im not dreaming, even though I believe Im awake?
Perception is more coherent
Couldnt perception be a coherent dream?
6. Vats and demons Maybe all my experiences are fed to me by a supercomputer
Maybe an evil demon controls my mind, and deceives me in everything I think
7. The conclusion We have no reason to think these scenarios are true. But they could be.
If they were true, our experience would be exactly as it is now, so we couldnt tell they were true. So we cant know that they are not true.
So our usual justifications for claiming that we know, e.g. there is an external material world, are insufficient.
8. Responses: Ryle Error logically presupposes correctness (you cant have counterfeit money unless there is real money)
This assumes scepticism claims we are mistaken; it doesnt, it claims we dont know (e.g. we dont know which beliefs are true, which in error)
The idea of error presupposes the idea of correctness - this doesnt mean any belief is ever correct (cp. perfection and imperfection)
9. Responses: ordinary language What know means is determined by how we usually use it. The sceptics claim that I dont know Im sitting here is nonsense - this is how the word know is learned.
But know also carries certain assumptions, e.g. that appearance is a good guide to reality; is this assumption justified?
10. Responses: Wittgenstein The sceptic undermines his own use of words: if I doubt whether I have a hand, can I be any more sure I know what hand means? But if I dont know what hand means, I cannot express the doubt.
But Wittgenstein also says that I dont know this is a hand - there is no further evidence or test. What I cant doubt I also cant know.