Premises:
No reciter is a stone.
No judge is a stone.
These do not determine whether reciters and judges overlap or are disjoint. Both classes merely exclude stones. Their common exclusion does not establish a relation between them.
Exclusion from a common class differs from establishing a relation between two classes. Two negative premises are not enough to give the intended syllogistic conclusion.
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The Fourth Figure: Productive Conditions, Moods and Proofs
Premises:
No reciter is a stone.
No judge is a stone.
These do not determine whether reciters and judges overlap or are disjoint. Both classes merely exclude stones. Their common exclusion does not establish a relation between them.
Exclusion from a common class differs from establishing a relation between two classes. Two negative premises are not enough to give the intended syllogistic conclusion.