The article presents the analyses of one of the aspects of the linguistic concept of the outstanding Castilian king and cultural figure of the 13th century Alfonso X the Learned, who is know for his encyclopedic knowledge, linguistic farsightedness and influence over European culture and science. The author of the article has focused on the analysis of the «grammar». Due to the absence in the extended work of the king of a separate study, dedicated to the linguistic matters, the research of the linguistic concept is based on a material of juridical and historical works: «Siete Partidas», «Septenario», «Estoria de Espanna», «General Estoria». Grammar – the most important of the seven liberal arts in the education system of the Early Middle Ages, gradually changes her position and suffers influence of logic during 11th-13th centuries. This affects also the ideas of Alfonso X, that combine the traditional approach to the grammar and logical influences, arrived from the universities of Chartres and Paris.