| First figure. | Third figure. | |
|---|---|---|
| M — G | M — G | |
| S — M | (Convert) | M — S |
| S — G | S — M |
Fourth. Converting the terms of both the major and minor premises of the first figure gives the fourth, as, e. g.:
| First figure. | Fourth figure. | |
|---|---|---|
| M — G | (Convert) | G — M |
| S — M | (Convert) | M — S |
| S — G | S — G |
To summarize: The second, third and fourth figures may be derived from the first. Converting the major premise of the first figure gives the second figure; converting the minor premise gives the third figure; and converting both premises gives the fourth figure.
2. THE MOODS OF THE SYLLOGISM.
By the mood of a syllogism is meant some particular arrangement of the propositions which compose the syllogisms. “Mood” stands for an arrangement of the propositions, while “figure” represents an arrangement of the terms in any syllogism.
Combining any three of the four logical propositions gives a mood, as, e. g., (1) E
A
E (2) A
I
I (3) E
I
O.
are moods. The first one has an E proposition for the major premise, an A for the minor and an E for the conclusion. This syllogism represents the first mood given above:
E No men are trees,
A All Americans are men,