لَوْ تَعْلَمُونَ عِلْمَ الْيَقِينِ
If you knew with knowledge of certainty. (التكاثر: 5)
ʿIlma al-yaqīn functions as an accusative verbal noun reinforcing the sense of taʿlamūn, while the genitive construction specifies the quality of that knowledge. Certainty here is not a mere vague possibility; it is a firmness of understanding that would transform the hearer’s response to the warning.
The two words are not purposeless synonymous padding. One describes the kind of knowing intended. The later expression ʿayna al-yaqīn brings direct sight into view and gives the passage a further rhetorical contrast.