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

PSY370: Thinking and Reasoning

LEC11 – Inference Insight and Relevance

Nov, 26th, 2009

Inference

! 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

validity

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

Names

Modus Ponens

Fallacy of

Affirming

Consequent

Fallacy of denying

antecedent

Modus Tollens

If P then Q

If P then Q

If P then Q

If P then Q

P

Q

not P

not Q

Therefore

Q

P

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

www.notesolution.com

fallacies of argument?

! experimentally study

Wason Selection Task

! might overtake the stroop effect as the most studied effect

Front

E

K

4

7

Back

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

card

! 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

Front

Drinking a Beer

Drinking a Coke

22 yrs of age

16 yrs of age

Back

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

! this is called CONTENT EFFECTS / THEMATIC EFFECTS

! 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

www.notesolution.com