A productive second-figure example is:
كل إنسان حيوان
Every human is an animal.
لا شيء من الحجر بحيوان
No stone is an animal.
فلا شيء من الإنسان بحجر
Therefore no human is a stone.
The middle term animal is affirmed of one subject and denied of the other. This difference in quality provides the exclusion required for a negative conclusion.
By contrast, two affirmatives can describe different subjects sharing an attribute, without establishing any identity between them.
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Semantic Fallacies: Defects of Matter, Form, and Predication
A productive second-figure example is:
كل إنسان حيوان
Every human is an animal.
لا شيء من الحجر بحيوان
No stone is an animal.
فلا شيء من الإنسان بحجر
Therefore no human is a stone.
The middle term animal is affirmed of one subject and denied of the other. This difference in quality provides the exclusion required for a negative conclusion.
By contrast, two affirmatives can describe different subjects sharing an attribute, without establishing any identity between them.