PSYC 213 Chapter Notes - Chapter 11: Kraft Dinner, Syllogism, Natural Deduction

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Published on 19 Nov 2012
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Chapter 11 Reasoning, Judgment, and Choice
By David Chak
1) Reasoning: Thought process that yields a conclusion from premises
(percepts, thoughts, or assertions)
2) Syllogistic logic (also known as Aristotelian or categorical reasoning) :
a. A syllogism consists of two premises and a conclusion.
b. Each of the premises specifies a relationship between the two
categories
c. Understanding different possible ways of interpreting a premise is
important
d. Four forms:
Universal Affirmative
All A are B
Interpretations:
All A are B but some B are not A
All A are B, then all B are A
Universal Negative
No A are B
Interpretation:
No A are B, no B are A are the same
Particular Affirmative
Some B are A
Interpretations:
Some A are B then some A are not B / Some B are
not A as well as some B are A
At least one B, and possibly all B are A
B
A,
B
A
A B
A
B
BA
A,
B
B
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Particular Negative
Some A are not B
Interpretations:
Some A are not B, then some B are not A
Some A are not B, then some A are B
At least one A, and possibly all A are not B
3) Logicism: The belief that logical reasoning is an essential part of human
nature
4) Practical syllogism: occurs when the conclusion drawn from two premises
becomes an action. (Henle, 1962/1968)
a. Premise 1: It is important for me to eat dinner
b. Premise 2: The only dinner I have in the fridge are kraft dinner
c. Conclusion: Therefore, it is important for me to eat kraft dinner
d. It is the natural mode of functioning of the conscious mind (Henle,
1962/1968)
5) Effect of content on Syllogistic Reasoning
a. People accept the conclusion to an invalid syllogism if they
believe that the conclusion is true in the real world (Galotti,
1989)
b. Effect of the participant’s beliefs is greater is syllogism is
invalid (Newstead,Pollard,Evans, Allen, 1992)
Participants initially determine whether or not the conclusion is
believable. If it is unbelievable, they try to find some ways of
thinking about the premises that renders the conclusion invalid.
If the conclusion is believable, they try to determine if there is
not some way to interpret the premises that makes the
conclusion acceptable.
6) Interpretation of some
a. People reason according to the specific way they interpret the
premises (Begg and Harris, 1982; Ceraso & Provitera, 1971)
AB
A
B
A B
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b. Interpretation of some is a good example of that, we ordinarily
interpret some as “some but not all” but logically, some means “at
least one, and possibly all”
7) Theory of syllogistic reasoning: mental models & natural deduction systems
8) People construct a mental model of the situation of which a set of premises
refers, and then draw conclusion that are consistent with the model (Johnson-
Laird, 1988)
9) Relational Reasoning:
a. Reasoning involving premises that express the relations between items
(transitive relations: A is bigger than B)
b. Linear syllogism / three-term series problem: two comparative
sentences from which a conclusion must be drawn. Eg, B < A, B > C,
then C is the smallest ( A > B > C)
c. Iconic: A principles of Johnson-Laird’s mental models theory: the
relations between the parts of the model correspond to the relations
between the parts of the situation it represents
d. Emergent consequences: You get more out of the mental model
than you put in (Johnson-Laird 2005)
e. Parsimony: People tend to construct only the simplest mental model
if possible (Johnson-Laird)
10) Natural deduction system makes use of propositions and deduction
rules to draw conclusions from these proposition.
11) Propositions are sentences built using connectives such as if…then,
and, or and not.
a. Entailing: proposition 1 is said to entail proposition 2 if proposition 1
follows from 2
b. p AND q entails p, q: coffee and tea available infers coffee avail, and
tea avail
c. p OR q and NOT p entails q: Coffee or Tea and not tea infers Coffee
d. The above two examples along with other rules are the elementary
inference principles that we rely on to solve reasoning problems
e. People carry out mental proofs to complete deduction tasks, conclusion
are derived
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