Lākin is another coordinating particle capable of expressing qasr in appropriate constructions. Its principal function is istidrāk: correcting an impression by supplying a contrasting attribution.
مَا زَيْدٌ شَاعِرًا، لَكِنْ خَطِيبٌ
Zayd is not a poet; rather, he is an orator.
This additional illustration negates the attribution of poetry and affirms oratory. The syntactic conditions of coordinating “lākin” matter. The mere presence of the word “but” does not automatically establish technical qasr.