Each premise has four possible categorical forms, so the minor and major yield 16 combinations.
First condition: qualities must differ. This eliminates eight pairs in which both are affirmative or both negative.
Second condition: the major must be universal. Of the eight remaining, four have a particular major and are eliminated.
Exactly four productive moods remain. It is important to identify not merely which moods work but which condition each invalid mood violates.
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The Second Figure: Conditions of Validity and Four Productive Moods
Each premise has four possible categorical forms, so the minor and major yield 16 combinations.
First condition: qualities must differ. This eliminates eight pairs in which both are affirmative or both negative.
Second condition: the major must be universal. Of the eight remaining, four have a particular major and are eliminated.
Exactly four productive moods remain. It is important to identify not merely which moods work but which condition each invalid mood violates.