Institutio Oratoria

By settling what a thing is we have come near to determining its identity, for our purpose is to produce a definition that is applicable to our case. Now the most important element in a definition is provided by quality, as, for example, in the question whether love be a form of madness. To this point

in our procedure belong those proofs which according to Cicero [*](Top. xxiii. 88. ) are peculiar to definition, that is, proofs drawn from antecedents, consequents, adjuncts, contraries, causes, effects and similarities, with the nature of which I have already dealt. [*](V. x. 73.)

I will, however, quote a passage from the pro Caecina [*](XV. 44.) in which Cicero includes brief proofs drawn from origins, causes, effects, antecedents and consequents:

Why then did they fly? Because they were afraid. What were they afraid of? Obviously of violence. Can you then deny the beginning, when you have admitted the end?

But he also argued from similarity: [*](XV. 43.)

Shall not that which is called violence in war be called violence in peace as well

Arguments may also be drawn from contraries, as for instance in the question whether a love-potion can be a poison, in view of the fact that a poison is not a love-potion. In order that my young students (and I call them mine, because the young student is always dear to me) may form a clearer conception of this second kind of definition, I will once more quote a fictitious controversial theme.