Skepticism: Do you know anything

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Skepticism Do you know anything?
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Skeptical Scenarios

• Morpheus Have you ever had a dream, Neo, that
  you were so sure was real?
• What if you were unable to wake from that dream?
  
• How would you know the difference between the
  dreamworld and the real world?

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Skeptical Scenarios (cont.)

• Descartes on Dreaming
• Descartes Evil Genius
• The Matrix
• The Truman Show
• Brain in a vat

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Main Idea of the Scenarios

• Things could be very different from how they
  seem
• Our experiences seem compatible with massive and
  systematic deception
• So how do we know were experiencing a real
  external world (as we think we are)?

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Skepticism

• Skepticism ordinarily means doubt
• Ex Im skeptical about the existence of
  ghosts.
• But skepticism in epistemology is a technical
  term for various views
• at a minimum a refusal to grant knowledge

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Kinds of Skepticism

• Practical skepticism (Pyrrhonian skepticism)
• a refusal to affirm or deny that we have
  knowledge
• Theoretical skepticism (Cartesian skepticism)
• the view that there is no knowledge
• Note Descartes wasnt a skeptic he just
  popularized discussion of this view.

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Kinds of Skepticism (cont.)

• Global skepticism
• the view that no one has any knowledge about
  anything (including this claim!)
• Local skepticism
• the view that there is no knowledge in some local
  domain (e.g. ethics, external world)
• Were concerned with
• local, theoretical skepticism about the external
  world

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Kinds of Skepticism (cont.)

• To make it specific, our Q is Do I know that
  the external world (things outside my own mind)
  are as they seem?
• Ex Do I know that I have hands?
• Ex Do I know that there are rocks?
• Skepticism No.
• Nonskepticism (dogmatism) Yes.

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Skeptics Brain-in-a-Vat Arg.

• You know you have hands only if you know youre
  not a brain in a vat (BIV).
• You dont know that youre not a BIV.
• ? You dont know that you have hands.

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Important Note

• The idea is this argument generalizes
• Nothing special about hands
• Problem arises for any similar proposition we
  claim to know about the external world
• So its supposed to establish theoretical
  skepticism about the external world

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Support for Premise 1 (S1)

• Exclusion Principle (EP)
• In order to know p, one must be able, on the
  basis of ones evidence, to rule out or exclude
  (and thus know to be false) any proposition that
  one knows to be incompatible with p.

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Support for Premise 2 (S2)

• Your evidence is compatible with being a BIV and
  not being a BIV
• Youd think you werent a BIV even if you were!
• Thats guaranteed by the setup of the scenario!

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Worries / Problems

• One could challenge S1
• But most of the action is in S2
• G. E. Moore famously argues against S2 with his
  reversal argument

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Moores Reversal Arg.

• You know you have hands only if you know youre
  not a brain in a vat (BIV).
• You do know that you have hands.
• ? You do know that youre not a BIV.

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Important Note

• Again, this argument generalizes
• So its supposed to refutetheoretical skepticism
  about the external world

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Support for Premise 1 (M1)

• Same as previous arg.
• Premise not as controversial
• Both sides accept it

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Support for Premise 2 (M2)

• You have every reason to believe you have hands
• Look down at them!
• Its highly unlikely that you are wrong and dont
  have hands
• Etc.

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Worry 1 Circularity

• Is Moore just denying the skeptics conclusion?
• Not if he gives independent support for P2
• And he does attempt to do so

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Response to Worry 1

• So how do we evaluate M2?
• Do we know we have hands?
• Certainly seems so
• We may have to rely on an account of the nature
  of knowledge

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Response to Worry 1 (cont.)

• Why not accept M2?
• We wouldnt accept M2 if we held JGTB
• But we saw that JGTB is too strong
• Can something weaker give you knowledge that you
  have hands?

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Worry 2 Ungers Criticism

• M2 is somewhat foolhardy and even dogmatic
• What is it to be foolhardy?
• to be recklessly bold, foolishly rash, etc.
• What is it to be dogmatic?
• to believe something stubbornly in the face of
  conflicting evidence, etc.

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Ungers Criticism (cont.)

• Thought experimentSuppose you claim to know you
  have hands, but you are then confronted by the
  evil scientist that hooked up your brain.
• Unger You would appropriately feel irrational
  and dogmatic.

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Ungers Criticism (cont.)

• You may say youre certain theres no scientist
  you have hands
• Youre right that you think youre certain
• And you may be right that theres no scientists
  you have hands
• But youre not (absolutely) certain

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Ungers Criticism (cont.)

• So you shouldnt say you know you have hands.
• You can believe it.
• Maybe youre justified in believing it.
• But dont say you know it.

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Potential Response to Unger

• Maybe were not absolutely certain you have
  hands ( theres no scientist)
• Our evidence doesnt guarantee it
• But who said we need absolute certainty for
  knowledge?!
• Unger seems to be assuming JGTB (which we saw is
  too strong)

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Response to Unger (cont.)

• Maybe we dont know for certain
• Maybe we dont know without a doubt
• But knowing something ? knowing something with
  certainty
• Were just interested in the former