The book proves this mood through conversion of the major premise. A universal negative converts to another universal negative.
Minor: All C are B.
Major: No A is B.
Converted major: No B is A.
Now in the first figure: All C are B; no B is A.
Conclusion: No C is A.
Conversion makes B the subject of the major, while it remains predicate of the minor. This gives the first-figure structure and demonstrates the required conclusion.
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The Second Figure: Conditions of Validity and Four Productive Moods
The book proves this mood through conversion of the major premise. A universal negative converts to another universal negative.
Minor: All C are B.
Major: No A is B.
Converted major: No B is A.
Now in the first figure: All C are B; no B is A.
Conclusion: No C is A.
Conversion makes B the subject of the major, while it remains predicate of the minor. This gives the first-figure structure and demonstrates the required conclusion.