Institutio Oratoria

Or we may give our opponent the choice between two alternatives of which one must necessarily be true, and as a result, whichever he chooses, lie will damage his case. Cicero does this in the pro Oppio: [*]( Oppius was accused of embezzling public money and plotting against the life of M. Aurelius Cotta, governor of Bithynia, where Oppius was serving as quaestor. Cicero's defence of him is lost. )

Was the weapon snatched from his hands when he had attacked Cotta, or when he was trying to commit suicide?

and in the pro Vareno: [*](See iv. ii. 26.)

You have a choice between two alternatives: either you must show that the choice of this route by Varenus was due to chance or that it was the result of this man's persuasion and inducement.

He then shows that either admission tells against his opponent. Sometimes again,

two propositions are stated of such a character that the admission of either involves the same conclusion, as in the sentence,

We must philosophise, even though we ought not,

or as in the common dilemma,

What is the use of a figure, [*](See vii. iv. 28, ix. i. 14, ix. ii. 65.) if its meaning is clear? And what is its use, if it is unintelligible?

or,

He who is capable of enduring pain will lie if tortured, and so will he who cannot endure pain.

As there are three divisions of time, so the order of events falls into three stages. For everything has a beginning, growth and consummation, as for instance

a quarrel, blows, murder. Thus arise arguments which lend each other mutual support; for the conclusion is inferred from the beginnings, as in the following case:

I cannot expect a purple-striped toga, when I see that the beginning of the web is black

; or the beginning may be inferred from the conclusion: for instance the fact that Sulla resigned the dictatorship is an argument that Sulla did not take up arms with the intention of establishing a tyranny.

Similarly from the growth of a situation we may infer either its beginning or its end, not only in questions of fact but as regards points of equity, such as whether the conclusion is referable to the beginning, that is,

Should the man that began the quarrel be regarded as guilty of the bloodshed with which it ended?

Arguments are also drawn from similarities: