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Syllogistic Reasoning
Thinking and Reasoning

The other key type of deductive reasoning is syllogistic reasoning,
which is based on the use of syllogisms.

Syllogisms are deductive arguments that involve drawing conclusions
from two premises (Maxwell, 2005; Rips, 1994, 1999).

All syllogisms comprise a major premise, a minor premise, and a
conclusion.
Syllogistic Reasoning
Erol ÖZÇELİK
Four kinds of premises

All humans are mortal.
Universal affirmative

No humans are perfect.
Universal negative

Some humans are healthy.
Particular affirmative

Some humans are healthy.
Particular negative

Major premise: All humans are mortal.

Minor premise: All Greeks are humans.

Conclusion:
All Greeks are mortal.
Atmosphere bias theory (Begg & Denny, 1969;
Woodworth & Sells, 1935)
1.
If there is at least one negative in the premises, people will
prefer a negative solution.
2.
If there is at least one particular in the premises, people
will prefer a particular solution. For example, if one of the
premises is “No pilots are children,” people will prefer a
solution that has the word no in it.

Nonetheless, the theory does not account very well for large
numbers of responses
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Research findings on syllogistic reasoning

In general, people tend to be slower and make more errors
when one or more premises are quantified by some or when
one or more premises are negative.

A syllogism presented in the order A-B, B-C (for example,
“Some red books are astronomy books. All astronomy books
are large.”) is much easier to work with than one presented
in the order or B-A, C-B (Johnson-Laird, 1975).
Mental models theory

Consider these premises:
Mental models theory

A mental model is an internal representation of information
that corresponds analogously with whatever is being
represented (see Johnson-Laird, 1983)

People reason by constructing models

Conclusions drawn by inspecting models

An attempt is made to construct alternative models that will
falsify the conclusion. In other words, there is a search for
counterexamples to the conclusion.

If no alternative models refute, draw inference as valid
conclusion
Mental models theory

Consider these premises:

All the squares are striped.

Some of the scientists are parents.

Some of the striped objects have bold borders.

All of the parents are drivers.

When the participant is asked to judge the
following conclusion,

When the participant is asked to judge
the following conclusion,
∴ Some of the squares have bold borders.

∴ Some of the scientists are drivers.

The participant inspects their mental model
and sees that, indeed, the conclusion is true in
that model.

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Mental models theory



The lamp is on the right of the pad.

The book is on the left of the pad.
The vase is in front of the lamp.

The greater the number of models needed in reasoning through
the problem, the more likely errors are to occur ( JohnsonLaird, Byrne, & Tabossi, 1989; Johnson-Laird & Steedman,
1978).

People make errors in reasoning because they overlook some of
the ways in which the premises might be true. For example, a
participant imagines Figure 10.3a as a realization of the
premises and overlooks the possibility of Figure 10.3b.
The clock is to the left of the vase.
Mental models

book

clock
pad
lamp
vase
The principle of truth

The construction of mental models involves the limited
processing resources of working memory
Conclusion



The clock is in front of the book.


Mental models theory
Premises
“Individuals minimise the load on working memory by tending
to construct mental models that represent explicitly only what is
true, and not what is false.”
Application in real life

A problem in the Chernobyl disaster was that, for several
hours, engineers failed to consider the possibility that the
reactor was no longer intact
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Belief bias (Evans et al., 1983)

All democrats support free speach

All dictators are not democrats

Therefore, all dictators donot support free speech

Invalid, but believable
Application in real life
Belief bias

Tendency to endorse arguments whose conclusions you believe,
regardless of whether they are valid or not.

Making illogical (invalid) conclusions that conform with prior
beliefs.
Application in real life: Informal
syllogistic reasoning

People can easily apply modus ponens arguments, but not
modus tollens arguments.

Susan: We are planning to go out tonight to a new club on the
river. Would you like to go with us?

Many people do not recognize the logical fallacies of denying
the antecedent or affirming the consequent, at least as these
fallacies are applied to abstract reasoning problems (Braine &
O’Brien, 1991; O’Brien, 2004; Rips, 1988,1994).

Steve: I’ve been to a couple of those clubs before, and I didn’t
like them. They were noisy, hot, and expensive. All those clubs
on the river are wastes of money. If I think a place is a waste of
money, I won’t go to it.

Will Steve go to the new club?
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Application in real life: Informal
syllogistic reasoning


“If I had mozzarella cheese, it would be in the refrigerator.
There is no mozzarella cheese in the refrigerator. Therefore, I
have no mozzarella cheese”).
Dual-Process Theories of Reasoning

There are two systems involved in reasoning, which means that there
is more than one way to respond to a reasoning problem.

Mistakes can occur if output from the wrong system is used as the
basis for responding.

Any task that demands logical thinking activates a fast intuitive
system which relies on general heuristics, including taking into
account context and similarity to previous problems (System 1); and a
slower, more analytical system that is sensitive to rules (System 2).

System 1 makes quick judgments based on a relatively superficial
analysis of the situation, so it does not carry out precise and detailed
reasoning processes.

System 2 works more slowly but more precisely, using explicit
reasoning processes to work through a problem on a step-by-step
basis.
Modus Tollens
 If
P, then Q
 Not
Q
 Not
P
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