A wāw-hollow verb has wāw as the second radical, as in قَالَ — يَقُولُ. A yāʾ-hollow verb has yāʾ there, as in بَاعَ — يَبِيعُ.
Both show alif in the third-person masculine singular perfect, yet their roots differ. This accounts for contrasting imperatives: قُلْ “say” versus بِعْ “sell.”
One must compare several inflected forms rather than treating every medial alif as evidence of one identical root.
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Distinguishing Wāw-Hollow and Yāʾ-Hollow Verbs
Hollow Verbs: Seven Iʿlāl Rules and Three Short Paradigms
A wāw-hollow verb has wāw as the second radical, as in قَالَ — يَقُولُ. A yāʾ-hollow verb has yāʾ there, as in بَاعَ — يَبِيعُ.
Both show alif in the third-person masculine singular perfect, yet their roots differ. This accounts for contrasting imperatives: قُلْ “say” versus بِعْ “sell.”
One must compare several inflected forms rather than treating every medial alif as evidence of one identical root.