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Lecture 11

PSY370H1 Lecture Notes - Lecture 11: Mental Model, Error Detection And Correction, Modus Tollens

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John Vervaeke

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PSY370: Thinking and Reasoning
LEC11 Inference Insight and Relevance
Nov, 26th, 2009
! use of evidence to alter belief so as to preserve truth
! looking for patterns that are truth preservative
! deduction: there are inference patterns that guarantee if the premises are true then the
conclusion must be true
! reasons cannot be valid, only arguments can be valid
! induction: if the premises are true this increase the probability that the conclusion will be true
! almost all evidence in science is inductive argument
! deduction is the paramount exemplar of how logic should operate: formal logic
! distinction b/w form and content in logic
Critical detachment
! A + B -> C
! are ppl able to see the invalid arguments which leads to a conclusion that agrees with their
personal conviction
! to do this they must be able to detach themselves from their personal view when assessing
Rules of formal logic
! forms of argument that will always produce the forms of argument that are valid
! fallacies: a logical characterization and psychological characterization
! logical: it is a pattern of inference that is invalid
! psychological: it is mistaken for being a valid argument
! has to be both invalid and you have to mistake it for a valid argument
! logic is normative: try to produce the best patterns for truth preserve
! logic is prescriptive: help us identify when we are making mistakes
! conditional reasoning: make use of if then relationship
! if A then B
! allows you to link thinks together in reasoning
! 4 basic patterns of conditional
Modus Ponens
Fallacy of
Fallacy of denying
Modus Tollens
If P then Q
If P then Q
If P then Q
If P then Q
not P
not Q
not Q
not P
! when ppl are reasoning do they use formal arguments of logic or are ppl. often taken in by
fallacious forms of argument
! if ppl's goal is to obtain/preserve truth and they are usually falling prey to fallacy, then prima
facie that would mean they are irrational
! this matters b/c if ppl were irrational then this would have lots of implication in psychology
! are humans rational in that they will reliably use logical form of argument and reliably avoid
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fallacies of argument?
! experimentally study
Wason Selection Task
! might overtake the stroop effect as the most studied effect
types of argument
(if you turned over
this card)
modus ponens
fallacy of affirming
the consequent
modus tollens
! you have to name the cards in order to test the following rule / truth of following statements:
! if there is a vowel on one side of the card then there is an even number on the other side of the
! ppl pick E and 4 to flip, falling to prey to the fallacy of affirming the consequent but they fail to
pick 7 which is a valid form of argument
! 10% of subjects get the correct answer (at best)
! why are ppl making these kinds of mistakes?
Griggs and Cox 1982
Drinking a Beer
Drinking a Coke
22 yrs of age
16 yrs of age
types of argument
modus ponens
fallacy of affirming
the consequent
modus tollens
! imagine you are a police officer on duty here is the rule
! if a person is drinking beer then he must be over 19yrs of age
! 72% correct response, ppl pick drinking a beer and 16yrs of age
! even though content does not determine validity, ppl are able to get better results when we
change content
! ppl are paying attention to content
! what are content effects and how do they facilitates reasoning?
Availability Thesis
! try to explain content effect, includes 2 parts: familiarity and concreteness
! when we give ppl common day content, this eases their cognitive load which can be used for
argument facilitation
! familiarity
! ppl done this before and remember the correct way of doing this
! concreteness
! give concrete example as opposed to abstract
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