“Grammar takes its name from the written character, as the derivation of the word indicates. The definition of grammar is this: Grammar is the science which teaches us to explain the poets and historians; it is the art which qualifies us to write and speak correctly. Grammar is the source and foundation of the liberal arts. It should be taught in every Christian school, since the art of writing and speaking correctly is attained through it.” Rhabanus Maurus, “Education of the Clergy,” in The Great Tradition: Classic Readings on What It Means to Be An Educated Human Being, ed. Richard M. Gamble. Wilmington 2007, p. 251 [Emphasis added]
Rhabanus Maurus (c.776-856) lived in early medieval Germany. He became a monk, schoolmaster, priest, abbot, and archbishop of Mainz. Rhabanus was one of the main theologians and authors of the Carolingian Renaissance. In this work he sought to define and preserve the liberal arts as a basis for the proper education of priests and pastors.
I wonder whether there is any correlation between grammatical aptitude and swearing. I have often observed that people who cannot express their thoughts in words due to their lack of understanding grammar often become frustrated, especially in a debate; they have thoughts, but cannot bring them out of infancy in the mind to actual expression on the lips and usually resort to cussing or giving up.