Rule 1: A moving wāw or yāʾ is replaced with alif when its preceding consonant bears fatḥah, subject to the appropriate morphological environment.
قَوَلَ → قَالَ — root ق و ل.
بَيَعَ → بَاعَ — root ب ي ع.
The alif does not tell us, by itself, whether the root had wāw or yāʾ. The imperfect gives vital evidence: يَقُولُ retains wāw and يَبِيعُ retains yāʾ.
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Rule 1: Wāw/Yāʾ Becomes Alif
Hollow Verbs: Seven Iʿlāl Rules and Three Short Paradigms
Rule 1: A moving wāw or yāʾ is replaced with alif when its preceding consonant bears fatḥah, subject to the appropriate morphological environment.
قَوَلَ → قَالَ — root ق و ل.
بَيَعَ → بَاعَ — root ب ي ع.
The alif does not tell us, by itself, whether the root had wāw or yāʾ. The imperfect gives vital evidence: يَقُولُ retains wāw and يَبِيعُ retains yāʾ.