Critical Thinking
Lecture 7a
Gettier
By David Kelsey
Defining Knowledge
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Knowledge:
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We saw in lecture 7 that knowledge is more than mere belief or even mere true belief.
Plato first defined knowledge as Justified True belief.
Knowledge as JTB
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Knowledge as JTB:
– Thus, S knows that p if and only if:
• S believes that p and
• P is true and
• S’s belief that p is justified
– Individually Necessary:
– Jointly sufficient:
Gettier &
Knowledge
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Edmund Gettier
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Born in 1927
Philosophy professor at University of Massachusetts Amherst since 1967
In his article Is Justified True Belief Knowledge? Gettier argues that something’s being
justified true belief is not a sufficient condition for it’s being knowledge.
• Thus, he argues that one can have a justified true belief and yet not have
knowledge.
• Gettier provides two counterexamples to prove his point.
Smith, the job &
10 coins
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Smith, the job & 10 coins:
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Smith believes that Jones is the man who will get the job and Jones has 10 coins in his
pocket.
• What is Smith’s justification for this belief?
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So Smith infers that it is true that The man who will get the job has ten coins in his
pocket.
• What is Smith’s justification for this belief?
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But Smith gets the job & he has 10 coins in his pocket
So Smith has JTB without knowledge!
The Ford &
Barcelona
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Now Smith gains evidence for the proposition:
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That Jones owns a Ford (‘F’)
• What’s Smith’s justification for this belief
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So Smith Infers: Either Jones owns a Ford or Brown is in Barcelona. (‘A’)
• What is Smith’s justification for this belief?
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But Jones doesn’t own a Ford and Brown is in Barcelona
• So Smith has JTB without knowledge again
Replies to Gettier
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Denying the assumptions:
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He assumes that:
• 1. It is possible for a person to be justified in believing a proposition that is false
• 2. Closure: for any proposition P, if S is justified in believing P and
– P entails Q &
– S deduces Q from P &
– S accepts Q as a result of this deduction, then
– S is justified in believing Q.
– Example:
» Snowing so Freezing
Denying Closure
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Denying closure:
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We could deny Closure by holding an Externalist theory of justification.
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For the Externalist, justification comes not from an inner mental state at all. Instead, it
is something external to your mind which confers justification on a belief.
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An Example:
• Reliabilism: a belief is justified if it is formed through a reliable belief forming
process
More replies to Gettier
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Accepting the counterexamples: We might also reply to Gettier by
accepting his counterexamples to the traditional definition of
knowledge.
– Finding another analysis: In this case we are then out to find a more
adequate analysis of KNOWLEDGE.
– Some examples:
• Infallible justification
• No false steps
• No defeaters
Last thoughts on
defining knowledge
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What Gettier shows is that there is a bigger problem with conceptual analysis
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A possible reply:
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concepts like knowledge have a graded nature