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Lecture 18: Reasoning
Fall 2009
Prof. Lombrozo
Overview of today’s class:
1. Deduction vs. Induction
2. Wason card selection task
3. One system or two (Rips, 2001)?
4. Midsemester evaluations
Reminder:
Assignment 7 due by Thurs @ 10pm
18.2
Reasoning at the
Computational level
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What is reasoning?
– Inferring from the known to the unknown
– “Going beyond the information given”
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What is the goal of reasoning?
– To acquire information that supports adaptive behavior
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Why is this a hard computational problem?
– Too much information: problem of deciding which information
is relevant
– Too little information: inferences are often underdetermined
18.3
Deduction
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Deduction
: process of reasoning in which the truth of
the premises guarantees the truth of the conclusion
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Validity
: an argument is valid if the truth of the
premises guarantees the truth of the conclusion
– Premises do not need to be true
– Depends only on form, not on content
If P, then Q.
P.
Q
Modus Ponens
If P, then Q.
~Q.
~P
Modus Tollens
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18.4
Induction
•
Induction
: process of reasoning in which the truth of
the premises affects the probability of the conclusion
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 Fall '09
 Lombrozo
 Logic, Inductive Reasoning, Modus ponens, Modus tollens, Wason, selection task

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