Institutio Oratoria

Arguments, then, may be drawn from definition, sometimes called finitio and sometimes finis. Definition is of two kinds. We may ask whether a particular quality is a virtue or make a definition precede and ask what is the nature of a virtue. Such a definition is either stated in general terms, such as Rhetoric is the science of speaking well, or in detail, such as Rhetoric is the science of correct conception, arrangement and utterance, coupled with a retentive memory and a dignified delivery.

we may define a word by giving its content as in the preceding instances, or by etymology: we may for instance explain assiduus [*]( Paulus (exc. Fest.) gives the following explanation of this absurd derivation, for which Cicero tells that Aelius Stilo was responsible: Some think that assiduus was originally the epithet applied to one who served in the army at his own expense, contributing an as ( i.e. instead of receiving it)! ) by deriving it from as and do, locuples [*](locheples ( wealthy ) is derived from locus = the posses sors of many places. ) by deriving it from copia locorum, pecuniosus [*](pecuniosus ( moneyed ) is derived from pecus = rich in herds. ) from copiapecorum. Genus, species, difference and property seem more especially to afford scope for definition, for we derive arguments from all of these.

Genus is of little use when we desire to prove a species, but of great value for its elimination. A tree is not necessarily a plane tree, but that which is not a tree is certainly not a plane tree; again, a virtue is not necessarily the virtue of justice, but that which is not a virtue is certainly not justice. We must proceed from the genus to the ultimate species; [*](cp. § 5. ) for example, to say that man is an animal will not suffice; for animal merely gives us the genus: nor yet will the addition of the words

subject to death