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
Assumptions Reality is logically distinct from appearance Evidentialism: justification depends on available evidence Infallibilism: knowledge requires not just that we aren’t mistaken, but that we couldn’t be
Perception Perceptual illusions –Illusions depend on veridical perception Stronger: we only perceive ‘appearances’ (sense-data) –We can’t know what reality outside the mind is like
Dreaming Can I know I’m not dreaming, even though I believe I’m awake? –Perception is more coherent –Couldn’t perception be a coherent dream?
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
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 couldn’t tell they were true. So we can’t 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.
Responses: Ryle Error logically presupposes correctness (you can’t have counterfeit money unless there is real money) –This assumes scepticism claims we are mistaken; it doesn’t, it claims we don’t know (e.g. we don’t know which beliefs are true, which in error) –The idea of error presupposes the idea of correctness - this doesn’t mean any belief is ever correct (cp. perfection and imperfection)
Responses: ordinary language What ‘know’ means is determined by how we usually use it. The sceptic’s claim that I don’t know I’m 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?
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 don’t know what ‘hand’ means, I cannot express the doubt. But Wittgenstein also says that I don’t know ‘this is a hand’ - there is no further evidence or test. What I can’t doubt I also can’t know.