In Book I, Isidore begins with a lengthy section on the first of three subjects in the mediaeval Trivium, considered at the time the core of essential knowledge, grammar. He covers the letters of the alphabet, parts of speech, accents, punctuation and other marks, shorthand and abbreviations, writing in cipher and sign language, types of mistake and histories. He derives the word for letters ("littera") from the Latin words for "to read" ("legere") and 'road' ("iter"), "as if the term were "legitera"", arguing that letters offer a road for people who read.