Quintilian, and J.S. Watson. Institutes of Oratory.Edited by Lee Honeycutt, 2010. Kindle Electronic Edition. Book V Chapter 8.
Aside from written and testimonial evidence in a case, Quintilian observes that there is a whole category of artificial proofs. Before detailing them, he shows “that there are certain qualities common to all kinds of proof” (Quintilian V.8.4). All arguments and proofs must follow orderly reasoning or be specific to the case at hand (Quintilian V.8.6). There are four different forms of proof: “because one thing is, another is not…; because there is one thing there is also another…; because one thing is not, another is…; because one thing is not, another is not” (Quintilian V.8.7). In future chapters Quintilian will explain these categories.