مَا زَيْدٌ إِلَّا كَاتِبٌ
Zayd is a writer, not a poet.
If the listener believes Zayd is a poet rather than a writer, “Zayd is only a writer” reverses that mistaken attribution. This is qasr al-qalb.
The same assertion belongs to different categories depending on the listener’s supposed view: believing “poet, not writer” calls for reversal, while believing “poet and writer together” calls for exclusion of joint attribution.