Like the other medieval Syriac grammars, the grammar of Bar Zubî is not aware of the notion of root. This paper shows that a grammar which makes uses only of concrete radicals appearing in the language, still allows a verbal classification and makes it possible to represent the relationship existing between the categories. The study deals with the formation of the active and of the passive in that perspective and announces a larger work of edition and of analysis of the grammar of Bar Zubî.