Quintilian, and J.S. Watson. Institutes of Oratory. Edited by Lee Honeycutt, 2010. Kindle Electronic Edition. Book I Chapter 4.
After a student has learned to read and write, Quintilian moves him to a study of grammar. He is not generally concerned about whether Greek or Latin is better, but inclines toward Greek. For this task all sorts of authors deserve study, not only poets but also writers of prose. Since grammar has to do with correct reading and expression it is critical to the study of rhetoric. A complete study of grammar includes meter, astronomy, and philosophy so as to be able to deal appropriately with a variety of subjects.
Quintilian now gives examples of Latin borrowing letters and sounds from Greek, including, interestingly enough, the digamma sound (Quintilian I.4.8). His illustrations of spelling and sounds may give us some insight into the sounds of Greek and Latin at his time.
In section 18 we begin a discussion of parts of speech. “As to their number, writers are by no means agreed. For the more ancient, among whom were Aristotle and Theodestes, said there were only verbs, nouns, and convinctions . . . the number was gradually increased” (Quintilian I.4.17-19).
Declining and conjugating is important “for otherwise they will never arrive at the understanding of what is to follow” (Quintilian I.4.22). He then illustrates a number of grammatical inquiries which can only be done after the essentials are mastered.