Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
My second reason was that indications, if indubitable, are not arguments, since they leave no room for question, while arguments are only possible in controversial matters. If on the other hand they are doubtful, they are not arguments, but require arguments to support them.
The two first species into which artificial proofs
This happens whenever there can be no doubt that something is being or has been done, or when it is impossible for it to be or have been done. In such cases there can be no dispute as to the fact. This kind of proof may be considered in connexion with past, present or future time.
For example, a woman who is delivered of a child must have had intercourse with a man, and the reference is to the past. When there is a high wind at sea, there must be waves, and the reference is to the present. When a man has received a wound in the heart, he is bound to die, and the reference is to the future. Nor again can there be a harvest where no seed has been sown, nor can a man be at Rome when he is at Athens, nor have been wounded by a sword when he has no scar. Some have the same force when reversed:
a man who breathes is alive, and a man who is alive breathes. Some again cannot be reversed: because he who walks moves it does not follow that he who moves walks.
So too a woman, who has not been delivered of a child, may have had intercourse with a man, there may be waves without a high wind, and a man may die without having received a wound in the heart. Similarly seed may be sown without a harvest resulting, a man, who was never at Athens, may
There are other indications or εἰκότα, that is probabilities, as the Greeks call them, which do not involve a necessary conclusion. These may not be sufficient in themselves to remove doubt, but may yet be of the greatest value when taken in conjunction with other indications.
The Latin equivalent of the Greek σημεῖον is signum, a sign, though some have called it indicium, an indication, or vestigium, a trace. Such signs or indications enable us to infer that something else has happened; blood for instance may lead us to infer that a murder has taken place. But bloodstains on a garment may be the result of the slaying of a victim at a sacrifice or of bleeding at the nose. Everyone who has a bloodstain on his clothes is not necessarily a murderer.