applicable role of laisa and layakun in the arabic grammar

since the verbs of and have similar use and play an important role in arabic grammar, it was useful to study both and discuss about their functions. following the discussion we found that there is five different functions for :first, it is an imperfect verb, (that give the noun an nominative case and the comment an objective case) arabic grammar experts disagree if it has a verb function or a noun one. second, as exceptive particles with maintenance its verb function (give the noun an nominative case and the comment an objective case) that here comment is an except. third, it is used as a conjunction that make negative sentence. forth, it has a negative function that means (ma). fifth, it can also be used as a conjugated perfect verb that was not common place in arabic grammar books, but we mentioned that function according to khalil ebn ahmad alfarahidi. quoting the reasons of grammarians about if it has a verb function or a noun function, we have concluded the discussion. we also identified the functions of : first, it is applying as a conjugated verb. second, it apply as an exceptive particle, as it is a non-derivative verb that its comment is an except. we hope that paper be useful in arabic grammar.