Institutio Oratoria

But whereas, if the question turns on some act of our own, we must make one statement and stick to it, if it turns on an act committed by others, we may cast suspicion on a number of different points. In certain controversial themes of the schools, however, in which it is assumed that we have put a question and received no reply, we are at liberty to enumerate all the possible answers that might have been given.

But we must remember only to invent such things as cannot be checked by evidence: I refer to occasions when we make our own minds speak (and we are the only persons who are in their secret) or put words in the mouth of the dead (for what they say is not liable to contradiction) or again in the mouth of someone whose interests are identical with ours (for he will not contradict), or finally in the mouth of our opponent (for he will not be believed if he does deny).

Glosses drawn from dreams and superstitions have long since lost their value, owing to the very ease with which they can be invented. But it will avail us little to use glosses in a statement of fact, unless they are consistent throughout the whole of our speech, more especially as certain things can only be proved by persistent assertion.