Deductive Reasoning

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Deductive Reasoning

• Psyc 494
• Talia Ben-Zeev

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Deductive Reasoning
Reasoning about premises and a conclusion with
certainty

If there is danger of earthquakes in SF Then
the city takes preventative measures.
There is danger of earthquakes in SF .
The city takes preventative measures.
modus ponens
If p then q.
p.
q
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Mental Proofs?

• Modus Ponens vs. Modus Shmomens

If there is danger of earthquakes in SF Then
the city takes preventative measures.
There is danger of earthquakes in SF .
The city does not take preventative measures.
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Are People Rational?
IF a card has a Vowel on one side THEN It has an
Even number on the other side
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Conditional Reasoning If p then q
If p then q. Modus Ponens p. q. If p then q.
Affirmation of the consequent q. p.
If p then q. Modus Tollens not q. not p. If
p then q. Denial of the antecedent not p. not q.

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The Wason Selection Task
Content effects on the W
ason Selection T
ask
(Griggs and Cox, 1982)
beer
coke
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If a person is drinking beer
, then the person must

be over 21
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The Wason Selection Task
If the form says entering on one side, then
the other side includes cholera among the list of
diseases (Cheng Holyoak, 1985)
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The Permission Schema the WST
Cheng and Holyaok (1985)
The permission schema
P1 If the action is to be taken (p), then
the precondition must be satisfied (q).
P2 If the action is not to be taken (not
-
p), then the precondition need not be
satisfied ( ).
P3 If the precondition is satisfied (q),
then the action may be taken ( ).
P4 If the precondition is not satisfied
(not-q), then the action must not be
taken (not-p).
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The WST Social Contracts
If a man eats cassava root, then he has a
tattoo Cosmides (1989)
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Perspective Effects
IF an employee works on the weekend, THEN That
person gets a day off during the week Gigerenzer
and Hug (1992)
Employee P not-Q Employer not-P and Q
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A non-deontic approach toPerspective effects
Staller, Sloman and Ben-Zeev (2000)
Week- day
Sun is shining
It is raining gray


Week- end

IF its a week-day THEN the sun is shining
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A non-deontic approach todeductive reasoning
Depressed individuals would do better on tasks
that disconfirm their beliefs (Ben-Zeev, in
progress)
I Make a
People still respect me
People lose respect for me



I Perform well
big mistake
IF I make a big mistake THEN people will still
respect me
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What is the appropriatenormative model?
Oaksford Chater (1994)
Hypothesis testing and the rarity assumption
ate

did not

did not

got
tripe
get sick
eat tripe
sick
If you eat tripe then you get sick
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Are people rational?
What do you think based on the studies that We
have discussed in this class so far?