Quintilian, and J.S. Watson. Institutes of Oratory. Edited by Lee Honeycutt, 2010. Kindle Electronic Edition. Book I Chapter 5.
Quintilian begins this chapter by discussing the excellences and faults of language (usage), “...all language has three kinds of excellence, to be correct, perspicuous, and elegant” (Quintilian I.5.1). Appropriate choice of words and their connections is critical to the work of the orator. Barbarisms may be introduced by borrowing words from other languages. They also come about by speaking in a cruel manner or mispronouncing words. Quintilian observes various difficulties which may occur in scansion of poetry but which may not be visible in prose. He also illustrates instances of placing an accent on the wrong syllable. It is also, of course, possible to import barbarism into language by making grammatical errors. As examples, Quintilian gives verbs in the wrong number. He then goes on to provide multiple examples of inadequate usage. Quintilian moves on (Quintilian I.5.61ff) to advocate changing foreign words entirely into Latin rather than retaining some of their forms from the original and adding Latin endings as needed.