فَإِنْ كَانَتْ وُقُوعَ النِّسْبَةِ بَيْنَ أَمْرَيْنِ أَوْ لَا وُقُوعَهَا فَحُصُولُهَا هُوَ التَّصْدِيقُ
If the issue is whether a relation between two things holds or fails to hold, establishing it is taṣdīq.
A complete predicative relation is one whose obtaining can be affirmed or denied. In “Zayd came,” the event of coming is predicated of Zayd; the question is whether this relation is true.
Taṣdīq does not merely seek the concepts “Zayd” and “coming.” It seeks a judgment about their relation. Accordingly, yes/no answers are the normal response to a pure question of assent.