Consider:
No horse is a stone.
No horse is a tree.
The middle, horse, is the subject of both premises, so the arrangement is third figure. But the premises establish no definite relation between stones and trees. Two classes excluded from the same class need not stand in any specific relation to each other.
The figure is present but the argument is not productive. Locating the middle is only the first step; quantity and quality conditions must also be checked.
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The Third Figure: Conditions and Six Productive Moods
Consider:
No horse is a stone.
No horse is a tree.
The middle, horse, is the subject of both premises, so the arrangement is third figure. But the premises establish no definite relation between stones and trees. Two classes excluded from the same class need not stand in any specific relation to each other.
The figure is present but the argument is not productive. Locating the middle is only the first step; quantity and quality conditions must also be checked.