Institutio Oratoria

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.