Negative tibaq juxtaposes affirmation and negation of one action or proposition. This differs from simply pairing two different opposite words; it places a single predication in opposed polarities.
«وَلَكِنَّ أَكْثَرَ النَّاسِ لَا يَعْلَمُونَ يَعْلَمُونَ ظَاهِرًا مِنَ الْحَيَاةِ الدُّنْيَا»
But most people do not know; they know only the outward aspect of worldly life.
The contrast distinguishes a deeper form of understanding, denied here, from limited knowledge of outward worldly matters. The affirmative and negative expressions produce the rhetorical force.