The core prohibitive structure is lā al-nāhiyah + jussive imperfect. In sound verbs, five person positions take sukūn, seven lose the inflectional nūn, and two feminine-plural positions retain nūn al-niswah. The internal vowel pattern distinguishes active from passive.
Word / formMeaning / explanation
لَا تَكْتُبْactive, second masculine singular, ordinary prohibition.
لَا تُكْتَبْpassive, second masculine singular, ordinary prohibition.
لَا تَكْتُبَنَّactive, same person, heavy nūn.
لَا تَكْتُبَنْactive, same person, light nūn.
Correct recognition uses the complete form, its vowels, person and final marker—not lā alone.