Productive example: Every cat is an animal. Every animal has a body. So every cat has a body. The minor premise places cats within animals.
Unproductive example: No cat is a bird. Every bird is an animal. We cannot infer that no cat is an animal: a cat can be an animal without being a bird.
A negative minor separates the minor term from the middle term. Thus the major premise's judgment about the middle does not transfer to the minor in the way required for first-figure inference.
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The First Figure: Conditions of Validity and Four Productive Moods
Productive example: Every cat is an animal. Every animal has a body. So every cat has a body. The minor premise places cats within animals.
Unproductive example: No cat is a bird. Every bird is an animal. We cannot infer that no cat is an animal: a cat can be an animal without being a bird.
A negative minor separates the minor term from the middle term. Thus the major premise's judgment about the middle does not transfer to the minor in the way required for first-figure inference.