Institutio Oratoria

[It is a false definition if you say,

A horse is a rational animal,

for though the horse is an animal, it is irrational. Again, a thing which is common to something else cannot be a property of the thing defined.] In the case under discussion, then, the accused alleges that the definition given by the accuser is false, whereas the accuser cannot do the same by his opponent's definition, since to steal a sacred object is undoubtedly sacrilege. He therefore alleges that the definition is too narrow and requires the addition of the words

or from a sacred place.

But the most effective method of establishing and refuting definitions is derived from the examination of properties and differences, and sometimes even from considerations of etymology, while all these considerations will, like others, find further support in equity and occasionally in conjecture. [*]( Conjecture is here used in the ordinary sense, not the technical. ) Etymology is rarely of assistance, but the following will provide an example of its use.

For what else is a 'tumult' but a disturbance of such violence as to give rise to abnormal alarm? And the name itself is derived from this fact.

[*]( Cic. Phil. VIII. i. 3. Tumultus is here used by Cicero in its special sense, civil war or Gallic invasion. He derives it from timor multus. )