Quintilian, and J.S. Watson. Institutes of Oratory. Edited by Lee Honeycutt, 2010. Kindle Electronic Edition. Book 8 Chapter 4.
In this chapter Quintilian discusses amplification and diminution. In amplification a stronger or more polarizing term is used to imply a more serious situation. For instance, a person is “beaten” rather than “hit” (Quintilian VIII.4.2). Quintilian categorizes amplification “in four ways; by augmentation, by comparison, by reasoning, and by accumulation” (Quintilian VIII.4.3). Augmentation escalates the actual offense to another level (Quintilian VIII.4.4). Comparison escalates the offence by drawing an unflattering parallel (Quintilian VIII.4.11). Amplification by reasoning takes a negative example and allows the listener to draw a comparison (Quintilian VIII.4.15). Quintilian gives many instances of descriptions which leave the reader to make either positive or negative inferences about the situation. Finally, by making multiple descriptions of a situation the author may create an accumulation of opinion either for or against a person or view (Quintilian VIII.4.26).
Extenuation is the opposite of amplification. In this, the speaker reverses the process to make a situation seem less serious than it actually is. The same methods are used, but the process reversed (Quintilian VIII.4.28). Quintilian finally notes that he considers hyperbole to be different in nature, though also useful to magnify or diminish.