Characterizing the relationship between the morphological and syntactic properties of sentences is essential for current linguistic theories, which indicate, for example, that morphological characteristics play a central role in determining the movement of the verb and the appearance of zero and expletive subjects. Faced with such a theory of skills, many questions arise about the role of these characteristics in performance, such as: is there a primordial role for the morpho-syntactic information of characteristics in parsing sentences? How is feature verification performed and at what stage of the analysis? The work addresses these issues with online and offline studies on understanding the subject-verb agreement in English. .