سَمِعَ — يَسْمَعُ and حَسِبَ — يَحْسِبُ both have kasrah on the second radical in the perfect, but differ in the imperfect.
Samiʿa class: فَعِلَ يَفْعَلُ — kasrah → fatḥah.
Ḥasiba class: فَعِلَ يَفْعِلُ — kasrah → kasrah.
The same contrast affects the second radical in their commands, اِسْمَعْ and اِحْسِبْ. The class therefore cannot be established solely from the perfect form or from the word's translation.
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Same perfect, different imperfect
Verb Classes and the Six Unaugmented Triliteral Patterns
سَمِعَ — يَسْمَعُ and حَسِبَ — يَحْسِبُ both have kasrah on the second radical in the perfect, but differ in the imperfect.
Samiʿa class: فَعِلَ يَفْعَلُ — kasrah → fatḥah.
Ḥasiba class: فَعِلَ يَفْعِلُ — kasrah → kasrah.
The same contrast affects the second radical in their commands, اِسْمَعْ and اِحْسِبْ. The class therefore cannot be established solely from the perfect form or from the word's translation.