Quintilian, and J.S. Watson. Institutes of Oratory.Edited by Lee Honeycutt, 2010. Kindle Electronic Edition. Book V Chapter 1.
Quintilian begins to consider proofs in Book Five. He cites Aristotle in a positive light, saying “that there are some proofs which an orator adopts that are unconnected with the art of speaking and others which he himself extracts and, as it were, produces from his cause” (Quintilian V.1.1). Many rhetoricians classify these as “inartificial” and “artificial.” The inartificial proofs are those which are supplied evidence of a factual or testimonial nature, though developed and governed by the orator (Quintilian V.1.2). At this point Quintilian does not discuss the artificial proofs. His goal is to show how the inartificial ones can be used (Quintilian V.1.3).