دُعِوَ → دُعِيَ
In the passive perfect the kasrah preceding underlying wāw licenses its change to yāʾ, also visible in دُعِيتُ.
مَدْعُوُوٌ → مَدْعُوٌّ
The root wāw meets the wāw of the passive-participle pattern; assimilation yields a doubled wāw.
Key distinction: دُعِيَ exemplifies weak-letter substitution; مَدْعُوٌّ shows assimilation. The morphological operations are not interchangeable.
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Morphological Explanation of the Passive and Participle
Defective Wāw Verb: Full Paradigm of دَعَا يَدْعُو with Morphological Explanations
دُعِوَ → دُعِيَ
In the passive perfect the kasrah preceding underlying wāw licenses its change to yāʾ, also visible in دُعِيتُ.
مَدْعُوُوٌ → مَدْعُوٌّ
The root wāw meets the wāw of the passive-participle pattern; assimilation yields a doubled wāw.
Key distinction: دُعِيَ exemplifies weak-letter substitution; مَدْعُوٌّ shows assimilation. The morphological operations are not interchangeable.