Two verbs may both be hollow wāw yet belong to different classes. قَالَ يَقُولُ retains a long ū in the imperfect, whereas خَافَ يَخَافُ has a long ā in the imperfect.
قَالَ — قُلْتُ — يَقُولُ — لَمْ يَقُلْ
خَافَ — خِفْتُ — يَخَافُ — لَمْ يَخَفْ
The root's medial wāw does not have to appear as a written wāw in every inflected form. The verb class and the conditions of weak-letter alteration determine the actual output.
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Two Hollow-Wāw Classes Contrasted
Complete Conjugation of Khāfa–Yakhāfu: Hollow Wāw from the Samiʿa Class
Two verbs may both be hollow wāw yet belong to different classes. قَالَ يَقُولُ retains a long ū in the imperfect, whereas خَافَ يَخَافُ has a long ā in the imperfect.
قَالَ — قُلْتُ — يَقُولُ — لَمْ يَقُلْ
خَافَ — خِفْتُ — يَخَافُ — لَمْ يَخَفْ
The root's medial wāw does not have to appear as a written wāw in every inflected form. The verb class and the conditions of weak-letter alteration determine the actual output.