The traditional weak letters are wāw (و), alif (ا), and yāʾ (ي). Their phonetic behavior can cause deletion, substitution, or vowel changes in particular word forms.
وَعَدَ contains wāw as an original radical.
قَالَ has a surface alif but the underlying root ق و ل.
بَاعَ has a surface alif but the underlying root ب ي ع.
Accordingly, the written alif of a form must not always be treated as the original radical. Morphological analysis identifies the underlying root and the change that produced the visible form.
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The Weak Letters
The Seven Morphological Classes: Sound, Hamzated, Weak and Doubled
The traditional weak letters are wāw (و), alif (ا), and yāʾ (ي). Their phonetic behavior can cause deletion, substitution, or vowel changes in particular word forms.
وَعَدَ contains wāw as an original radical.
قَالَ has a surface alif but the underlying root ق و ل.
بَاعَ has a surface alif but the underlying root ب ي ع.
Accordingly, the written alif of a form must not always be treated as the original radical. Morphological analysis identifies the underlying root and the change that produced the visible form.