In the schematic root فَعَلَ, fāʾ, ʿayn and lām represent the first, second and third radicals. They are called fāʾ al-kalimah, ʿayn al-kalimah and lām al-kalimah.
For نَصَرَ, nūn is the first, ṣād the second and rāʾ the third radical.
For سَمِعَ, sīn, mīm and ʿayn occupy these places.
For ضَرَبَ, they are ḍād, rāʾ and bāʾ.
The decisive vowel for these classes is the second radical's vowel in the perfect/imperfect pair.
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The fāʾ–ʿayn–lām template
Verb Classes and the Six Unaugmented Triliteral Patterns
In the schematic root فَعَلَ, fāʾ, ʿayn and lām represent the first, second and third radicals. They are called fāʾ al-kalimah, ʿayn al-kalimah and lām al-kalimah.
For نَصَرَ, nūn is the first, ṣād the second and rāʾ the third radical.
For سَمِعَ, sīn, mīm and ʿayn occupy these places.
For ضَرَبَ, they are ḍād, rāʾ and bāʾ.
The decisive vowel for these classes is the second radical's vowel in the perfect/imperfect pair.