مَا زَيْدٌ إِلَّا شَاعِرٌ / إِنَّمَا زَيْدٌ شَاعِرٌ
Zayd is nothing but a poet / Zayd is only a poet.
Both may restrict the same predication, but negation–exception overtly marks rejection and exception; innamā carries the restrictive effect in a compact construction. Their optimal use depends on the addressee’s assumptions.
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Qasr by Coordination, Negation–Exception, and Innamā
مَا زَيْدٌ إِلَّا شَاعِرٌ / إِنَّمَا زَيْدٌ شَاعِرٌ
Zayd is nothing but a poet / Zayd is only a poet.
Both may restrict the same predication, but negation–exception overtly marks rejection and exception; innamā carries the restrictive effect in a compact construction. Their optimal use depends on the addressee’s assumptions.