Quintilian, and J.S. Watson. Institutes of Oratory.Edited by Lee Honeycutt, 2010. Kindle Electronic Edition. Book V Chapter 10.
In this rather lengthy chapter Quintilian discusses name and types of arguments. He observes that the various names for arguments used among Greek rhetoricians are basically synonymous, with only minor shades of difference (Quintilian V.10.1). He proceeds to discuss the shades of distinction made by different authors.
“Since, then, argument is a process of reasoning affording a proof, by which one thing is gathered from another, and which establishes what is doubtful y reference to what is certain, there must assuredly be something in a cause that does not require proof” (Quintilian V.10.11). The information that does not need proof serves as a foundation to achieve further proofs. From this information the argument can grow in one of two ways. Some arguments pertain to things and some to persons. They are treated differently (Quintilian V.10.23). Quintilian lists several ways in which he considers people different from one another. Arguments from things are very important as well (Quintilian V.10.32). This is where we find motives to action (Quintilian V.10.34). Quintilian repeatedly emphasizes the complexity of cases, which may include extenuating or mitigating circumstances. Especially important is the time frame surrounding evidence and testimony (Quintilian V.10.42). Though the cases are diverse, “three points are doubtless to be considered, whether it is, what it is, and of what nature it is” (Quintilian V.10.53). The arguments throughout the case are built on these three questions. The logical argument will therefore consider the identity of the issue (Quintilian V.1.56). Quintilian illustrates various proofs of identity. Additionally, the argument will have a natural structure which will progress in a natural manner (Quintilian V.10.71). This requires also that the rhetorician must understand and use appropriate dialectic structures (Quintilian V.10.81).
All in all, Quintilian concludes that arguments are varied and complex enough that they cannot be cataloged completely (Quintilian V.10.100). As a result, the best practice is to consider the case carefully and identify the important variables individually.