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DEDUCTION: Part 3 -
Page 1-b
Figures
and Moods of
The Categorical Syllogism
by Jonathan Dolhenty, Ph.D.
Rules for the
Syllogistic Figures
The First
Figure
The middle term (M) is the subject of the major
premise and the predicate of the minor premise.
The rule for the First Figure is: The minor
premise must be affirmative and the major premise
must be universal.
Explanation of
the Rule
First Part: The minor premise must
be affirmative.
If the minor premise is negative, the conclusion
must then be negative (according to General Rule
Number 7) and the major term (P) in the conclusion
would be universal. If, however, the minor premise
is negative, then the major premise would have to
be affirmative.
Both premises are not allowed to be negative
(according to General Rule Number 6). Thus the
major term (P) would be particular in the major
premise, since it is the predicate of an
affirmative sentence.
In that case, the major term (P) would be
particular in the premise and universal in the
conclusion. This violates General Rule Number 2. In
order to avoid an illicit major, the minor
premise must be affirmative.
Second Part: The major premise
must be universal.
If the major premise is particular, the middle
term (M) would be a particular term, since it is
the subject of this proposition. The minor premise
in this figure, however, must be affirmative, in
order to be in accord with the first part of this
rule.
The middle term (M), because it is the predicate
of the minor premise, will be particular here also.
If, therefore, the major premise is particular, the
middle term (M) would be particular in both
premises. But this would entail an undistributed
middle and violate General Rule Number 4.
The only means by which to get a distributed
middle is to make the major premise universal. This
shows, then, that the second part of the rule is
correct: The major premise must be universal.
The Valid Moods
of the First Figure
When we consider the moods which are valid for
the syllogisms of the First Figure, we find that
four of the eight possible legitimate combinations
are valid and four are invalid. Here are the
diagrams:
|
Moods of
the First Figure
|
|
A
|
uM
|
+
|
pP
|
|
A
|
uS
|
+
|
pM
|
|
|
uS
|
+
|
pP
|
|
|
Valid
|
|
|
A
|
uM
|
+
|
pP
|
|
E
|
uS
|
-
|
uM
|
|
|
uS
|
-
|
uP
|
|
|
Illicit
Major
|
|
|
A
|
uM
|
+
|
pP
|
|
I
|
pS
|
+
|
pM
|
|
|
pS
|
+
|
pP
|
|
|
Valid
|
|
|
A
|
uM
|
+
|
pP
|
|
O
|
pS
|
-
|
uM
|
|
|
pS
|
-
|
uP
|
|
|
Illicit
Major
|
|
|
E
|
uM
|
+
|
uP
|
|
A
|
uS
|
+
|
pM
|
|
|
uS
|
-
|
uP
|
|
|
Valid
|
|
|
E
|
uM
|
-
|
uP
|
|
I
|
pS
|
+
|
pM
|
|
|
pS
|
-
|
uP
|
|
|
Valid
|
|
|
I
|
pM
|
+
|
pP
|
|
A
|
uS
|
+
|
pM
|
|
|
uS
|
+
|
pP
|
|
|
Undist.Middle
|
|
|
O
|
pM
|
-
|
uP
|
|
A
|
uS
|
+
|
pM
|
|
|
uS
|
-
|
uP
|
|
|
Undist.Middle
|
|
Clearly, there are only four valid moods for the
First Figure: A A, A I, E A, and E I. Each one
follows the rule that the minor premise must be
affirmative and the major premise must be
universal.
The A E and A O moods are invalid because of an
illicit major brought into the conclusion.
They violate the first part of the rule: The minor
premise must be affirmative.
The I A and O A moods are invalid because an
undistributed middle is the result of the
arrangement and this violates the second part of
the rule: The major premise must be universal.
Here are some arguments which illustrate the
valid moods for the First Figure:
|
A
|
Every human being should have equal
rights.
|
|
A
|
Women are human beings.
|
|
|
Therefore, Women should have equal
rights.
|
|
A
|
All politicians are great
talkers.
|
|
I
|
Some lawyers are
politicians.
|
|
|
Therefore, Some lawyers are great
talkers.
|
|
E
|
No mammals are cold-blooded.
|
|
A
|
All dogs are mammals.
|
|
|
Therefore, No dogs are
cold-blooded.
|
|
E
|
No misers are generous.
|
|
I
|
Some wealthy people are
misers.
|
|
|
Therefore, some wealthy people are
not generous.
|
To Page
1-c of Figures and Moods of the Syllogism
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