enquiriesalevelphilosophycouk Michael Lacewing Am I a brain in a vat Knowledge is not belief even true belief Are my reasons for my beliefs sufficient for knowledge Maybe all my experiences are fed to me by a supercomputer ID: 635179
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Slide1
Scepticism
Michael Lacewingenquiries@alevelphilosophy.co.uk
© Michael LacewingSlide2
Am I a brain in a vat?
Knowledge is not belief (even true belief)Are my reasons for my beliefs sufficient for knowledge?
Maybe all my experiences are fed to me by a supercomputer
© Michael LacewingSlide3
The sceptical challenge
If I am a brain in a vat, my beliefs about the world are mostly falseIf I were a brain in a vat, my experience would be exactly the same as if I were notSo I cannot know that I am not a brain in a vat
I have no reason to believe that I am not a brain in a vat
So, my beliefs about the world are not justified (even if I’m not a brain in a vat)
© Michael LacewingSlide4
What philosophical scepticism is
‘I have two hands’But how do I know that appearance is a reliable guide to reality?
This is not an ‘everyday’ doubt
Nor need it have practical consequences
Nor does scepticism just attack
certainty
‘
Nothing is known’
Is this claim itself known
?
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What philosophical scepticism is
Our beliefs are all falseNot 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
So we don’t have
knowledge
Local scepticism: scepticism about some specific claim or area of knowledge
Global scepticism: scepticism about all knowledge claims, esp. the world outside the mind
© Michael LacewingSlide6
Descartes’ three ‘waves’ of doubt
I can be deceived by our senses.
I cannot know that I am not dreaming.
I could be deceived even in very simple thoughts by an evil demon.
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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.
© Michael LacewingSlide8
Empiricism
Our knowledge is limited to(a priori) knowledge of analytic propositions and what can be deduced from them
(a posteriori) knowledge of synthetic propositions about the world outside one’s
minds
knowledge of our own minds, derived from impressions of
reflectionThis can lead to local scepticism re. God and morality
We must infer the existence of physical objects as the ‘best explanation’ for our experience
© Michael LacewingSlide9
Objections
Descartes: if empiricism is true, then physical objects remain a hypothesis, not knowledgeBut does Descartes (and scepticism) require too much of knowledge?Physical objects are not the best explanation of our experience
If we were brains in vats, this would also explain our experience equally well
Perhaps
something
external to our minds exists, but we cannot know what
© Michael LacewingSlide10
Berkeley’s response
The concept of physical objects makes no senseReply to scepticism by removing the appearance/reality
distinction
In experiencing ideas, we are experiencing reality
The role of God is a bit like the role of the computer in brains in vats!
© Michael LacewingSlide11
Reliabilism
Scepticism assumes that knowledge needs justification, and we don’t have itReliabilism rejects the need for justificationI
f my beliefs are caused by a reliable process, and are true, then I have knowledge
If I am not a brain in a vat, then perception is reliable, and I know about the physical world I experience
But do I know that I am not a brain in a vat?
I don’t need to know this to know about physical objects
Why assume that I must know that I know that p in order to know that p?
I don’t need to
know
that process that causes my beliefs is reliable
© Michael Lacewing