Institutio Oratoria

Whichever of these two forms we employ, we must take care, first that our fiction is within the bounds of possibility, secondly that it is consistent with the persons, dates and places involved and thirdly that it presents a character and sequence that are not beyond belief: if possible, it should be connected with something that is admittedly true and should be supported by some argument that forms part of the actual case. For if we draw our fictions entirely from circumstances lying outside the case, the liberty which we have taken in resorting to falsehood will stand revealed.

Above all we must see that we do not contradict ourselves, a slip which is far from rare on the part of spinners of fiction: for some things may put a most favourable complexion on portions of our case, and yet fail to agree as a whole. Further, what we say

In either case the orator should bear clearly in mind throughout his whole speech what the fiction is to which he has committed himself, since we are apt to forget our falsehoods, and there is no doubt about the truth of the proverb that a liar should have a good memory.