This study tackles the morphological reasoning in ibn Jiniis linguistic lesson in his book Morphological phenomena characteristics, which represents the intellectual maturity of his linguistic lesson, and the study is proceeded in two basic aspects, the first aspect is the morphological reasoning of linguistic issues in general, the second aspect is the morphological issues that are addressed according to morphological and grammatical reasoning. This was addressed with lessons, analysis, statements and clarification by taking advantage of the views of former scholars such as khaleel, Sibawayh, Al-Marbar, Ibn al-Sarraj and Abu Ali al-Farisi, as well as the opinions of subsequent scholars such as Al-Radhi, Al-Syoti and others Ibn Jinii brought up the problematic issues of morphological structures, whether they were verbs or nouns, and then proceeded to explain this problem in accordance with specific rules based on the nature of the hearing in linguistic use in Arabic, from the mental statement based on assessment as an asset derived from the structures, a rule of extract passive voice from the active voice, as well as measurement of general rules, in order to take into account the synonym, acronym, , to say in the continuity, anomalies and others.