وَإِنَّمَا يُرْجَى بَعْضُ الْمَنْفَعَةِ فِي الِاسْتِكْثَارِ مِنْ هَذَا الشَّأْنِ، وَجَمْعِ الْمُكَرَّرَاتِ مِنْهُ لِخَاصَّةٍ مِنَ النَّاسِ مِمَّنْ رُزِقَ فِيهِ بَعْضَ التَّيَقُّظِ، وَالْمَعْرِفَةِ بِأَسْبَابِهِ وَعِلَلِهِ،
Some benefit from gathering many reports and repeated routes is expected for specialists with alert judgment and knowledge of the causes and defects of transmission.
Turuq are distinct routes through which a report is transmitted. Their comparison may uncover an addition, a variant wording, or a mistaken attribution within a chain. An ʿillah can be an effective defect in an apparently sound chain or text; not every difference is such a defect.
At this point al-Nawawī stresses investigation of both meanings and the sciences of isnād and ʿilal. A defect can concern either the chain or the wording; an isolated route may conceal a problem visible only through comparison.