Defective Verbs

Defective (final-weak) verbs end in a weak letter: مشى (to walk), دعا (to invite), نسي (to forget), اشترى (to buy), انتهى (to end).

• Past with a consonant ending: the weak letter shows as ي or و: مشيت، اشترينا، دعونا، نسيت.
• Past with ت (she) or وا (they): verbs ending in ى or ا drop the last letter (مشت، دعت، اشتروا); verbs like نسي keep ي for she (نسيت) but drop it for they (نسوا).
• Present: يمشي، يشتري، يدعو end in a long vowel, and verbs like نسي and بقي end in ى: ينسى، نبقى.
• After لم and after لا meaning "don't", the final long vowel is cut: لم ينس (he didn't forget), لا تنس (don't forget), لم أشتر (I didn't buy).
• Endings stay in these forms: لا تبكي (don't cry, to a woman), لم يبقوا (they didn't stay).