Both samiʿa and fataḥa have imperfect يَفْعَلُ, yet different perfects:
سَمِعَ يَسْمَعُ — kasrah on the second radical in the perfect, fatḥah in the imperfect.
فَتَحَ يَفْتَحُ — fatḥah on that radical in both forms.
Therefore the imperfect يَسْمَعُ must not be classified as the fataḥa class solely because it matches yafʿalu. The complete verb pair identifies the class.
The verbal nouns also need to be learned as attested forms: سَمْعٌ and فَتْحٌ.
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Contrasting samiʿa and fataḥa
Verb Classes and the Six Unaugmented Triliteral Patterns
Both samiʿa and fataḥa have imperfect يَفْعَلُ, yet different perfects:
سَمِعَ يَسْمَعُ — kasrah on the second radical in the perfect, fatḥah in the imperfect.
فَتَحَ يَفْتَحُ — fatḥah on that radical in both forms.
Therefore the imperfect يَسْمَعُ must not be classified as the fataḥa class solely because it matches yafʿalu. The complete verb pair identifies the class.
The verbal nouns also need to be learned as attested forms: سَمْعٌ and فَتْحٌ.