Institutio Oratoria

For witnesses and investigation and the like all make some pronouncement on the actual matter under trial, whereas arguments drawn from without are in themselves useless, unless the pleader has the wit to apply them in such a manner as to support the points which he is trying to make.

Such in the main are the views about proof which I have either heard from others or learned by experience. I would not venture to assert that this is all there is to be said; indeed I would exhort students to make further researches on the subject, for I admit the possibilities of making further discoveries. Still anything that may be discovered will not differ greatly from what I have said here.

It has generally been laid down that an argument to be effective must be based on certainty; for it is obviously impossible to prove what is doubtful by what is no less doubtful. Still some things which are adduced as proof require proof themselves.

You killed your husband, for you were an adulteress.

Your javelin was found in the body of the murdered man.