Traditional Logic I Chapter XII - Memoria Press

Three Acts of the Mind
Mental Act:
• Simple Apprehension
• Judgment
• Deductive Inference
Verbal Expression:
• Term
• Proposition
• Syllogism
Slide 12-1
The Three
Categories of
Rules of
Validity
Terminological
Quantitative
Qualitative
Slide 12-2

Quantitative
Rules of
Validity
III. If a term is distributed in the
conclusion, then it must be
distributed in the premises.
IV. The middle term must be
distributed at least once.
Slide 12-3
Quantitative
Rules
These two rules are quantitative
because they have to do with the
quantity of the statements in the
syllogism. (Universal or Particular)
Slide 12-4

Rule III: If a term is distributed
in the conclusion, then it must
be distributed in the premises.
Slide 12-5
This rule prevents
us from trying to say
more in the
conclusion than is
justified by the
premises.
The Definition
of
Distribution
Distribution is the status of a
term in regard to extension.
Slide 12-6

Diagram of the
Distribution of
Terms
Type of Sentence Subject-Term Predicate-Term
A
I
E
O
Distributed
Undistributed
Distributed
Undistributed
Undistributed
Undistributed
Distributed
Distributed
Slide 12-7
Application of
Rule III
All angels Md are spiritual beings Pu
No men Sd are angels Md
Therefore, no men Sd are spiritual beings Pd
Slide 12-8

The Fallacy of Illicit Process
Slide 12-9
This fallacy is committed
when the extension of a
term is greater in the
conclusion than in the
premises. In other
words, the conclusion
says more than is
justified by the premises.
Two kinds of
Fallacy of Illicit
Process
The Fallacy of Illicit Major
The Fallacy of Illicit Minor
Slide 12-10

The Fallacy of Illicit Major
Slide 12-11
This fallacy is committed
when the major term has
greater extension in the
conclusion than in the
premises—i.e. when the
major term is distributed
in the conclusion but not
the premises.
The Fallacy of Illicit Major
All angels Md are spiritual beings Pu
No men Sd are angels Md
Therefore, no men Sd are spiritual beings Pd
Slide 12-12

Slide 12-13
Possibility #2
(premises true &
conclusion false:
Possibility #1
(premises true&
conclusion true):
Spiritual
Beings
Spiritual
Beings
Angels
Men
Angels
Men
All angels Md are spiritual beings Pu
No men Sd are angels Md
Therefore, no men Sd are
spiritual beings Pd
The Fallacy of Illicit Minor
Slide 12-14
This fallacy is
committed when the
minor term has
greater extension in
the conclusion than in
the premises—i.e.
when the minor term
is distributed in the
conclusion but not the
premises.

The Fallacy of Illicit Minor
All men Md are animals Pu
All men Md are mortal Su
Therefore, all mortals Sd are animals Pu
Slide 12-15
Possibility #1
Slide 12-16
(premises true&
conclusion true):
Possibility #2
(premises true &
conclusion false):
Mortals
Animals
Mortal
Men
Animals
Men
All men Md are animals Pu
All men Md are mortal Su
Therefore, all mortals Sd are
animals Pu

Quantitative
Rules of
Validity
III. If a term is distributed in the
conclusion, then it must be
distributed in the premises.
IV. The middle term must be
distributed at least once.
Slide 12-17
Rule IV: The middle term must
be distributed at least once
Slide 12-18
An undistributed middle
term cannot connect
the minor and major
terms together, since
at least one of either
the minor or major
term will refer to all of
a particular thing.

Rule IV: The middle term must
be distributed at least once
All angels Pd are spiritual beings Mu
All men Sd are spiritual beings Mu
Therefore, all men Sd are angels Pu
Slide 12-19
Slide 12-20
Possibility #2
(premises true &
conclusion false:
Possibility #1
(premises true&
conclusion true):
Spiritual Beings
Spiritual Beings
Angels
Angels
Men
Men
All angels Pd are spiritual beings Mu
All men Sd are spiritual beings Mu
Therefore, all men Sd are angels Pu

Quantitative
Rules of
Validity
III. If a term is distributed in the
conclusion, then it must be
distributed in the premises.
IV. The middle term must be
distributed at least once.
Slide 12-21