# 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

•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

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