Quintilian, and J.S. Watson. Institutes of Oratory.Edited by Lee Honeycutt, 2010. Kindle Electronic Edition. Book V Chapter 9.
Quintilian continues his discussion of proofs by observing that “indications” are not actual arguments (Quintilian V.9.1). An argument is devised by the orator and could potentially be overcome. A sign, or indication is a physical piece of evidence so its existence cannot be removed (Quintilian V.9.2). A sign, therefore, is a kind of proof rather than an argument (Quintilian V.9.4-5). Some signs bear more force when used in an argument. Regardless, the argument itself must be applied. Again, some indications point very strongly to a conclusion (Quintilian V.9.8). Yet even a strong sign, such as a blood-soaked garment, may not be an indicator of an actual murder. It requires additional support (Quintilian V.9.11). Quintilian continues with a number of signs which do not lead to certain conclusions.