1. The verb (not to be) – لَيْسَ   It is used only in the perfect tense and gives the meaning of the imperfect. Like كَانَ (noun or adjective) of لَيْسَ will be الْمَنْصُوبُ (accusative case). Past tense conjugation of لَيْسَ:     3rd person masculine   Singular Dual Plural لَيْسَ لَيْسَا لَيْسُوْا   3rd