"> This investigation is a critical approach on one of the mostimportant linguistic material of the Arabic grammarian (i.e. Poetry)which has been used to justify the grammatical categories. The centraldiscussion related to the difference between poetry and prose as aspecial structure that can’t be the proper patterns for derivation ofgrammatical rules. In the formalism perspective literariness meansmaking-strange that take place on typical language. This processdepends on several mechanisms such as the rhyme, putting the wordsforward and backward, deleted, addition, and changing the position ofthe phrase in poetic context. These mechanism have been called(poetic necessities) or (zarorat Al sheriya) in the Arabic traditionallinguistic. Our hypothesis is the poetic language has not sufficientauthenticity to be used as a well form structure. But the grammarianconsidered it as a well-form structure that has validity to be usedbroadly in the derivation of grammatical rules. Controversially poetryloses its authenticity because of its abnormality. Indiscriminationbetween the poetry and prose in Arabic grammatical studies haveleaded to the expansion of grammatical exceptional case andconsequently this procedure created very serious complexity andambiguity in the Arabic grammar