Quintilian, and J.S. Watson. Institutes of Oratory.Edited by Lee Honeycutt, 2010. Kindle Electronic Edition. Book V Chapter 11.
Quintilian now discusses a third group of proofs, which he identifies as paradeigmata. These are generally examples of like things (Quintilian V.11.1). However, there may be more disparate comparisons in these examples as well. Again, different teachers of rhetoric divide the field in various ways. Regardless, all arguments are based on “things similar, dissimilar, or contrary” (Quintilian V.11.5). Yet a parallel example is very persuasive. Quintilian gives several illustrations of this. Some examples are not parallel but show a relationship of greater and less. These are of great effect (Quintilian V.11.10). Again, examples follow. The illustration in a speech may be lengthy, retelling a substantial piece of narrative (Quintilian V.11.15).
If an example is not available, a comparison may be effective (Quintilian V.11.22). The comparison (parabole) is not as clearly parallel. Quintilian illustrates several comparisons. A less effective proof is the “icon” in which the appearance of something is used in the illustration.
All these proofs are vulnerable to attack. They have weak points including the authority on which they rest (Quintilian V.11.36). Again, Quintilian gives examples of stronger and weaker authorities.