Institutio Oratoria

Quintilian

Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.

This is the less surprising, since the nature of verbs is such that we often express the active by the passive form, as in the case of arbitror (think) and suspicor (suspect), and the passive by the active, as in the case of vapulo (am beaten). Consequently the interchange of the two forms is of common occurrence, and in many cases either form can be used: for example, we may say luxuriatur or luxuriat (luxuriate), fluctuatur or fluctuat (fluctuate), adsentior or adsentio (agree). Figures also occur in connexion with number,

as

v7-9 p.447
when the plural follows the singular, as in the phrase gladio pugnacissima gens Romani (the Romans are a nation that fight fiercely with the sword); for gens is a singular noun indicating multitude. Or the singular may follow the plural, as in the following instance,
  1. qui non risere parentes
  2. nec deus hunc mensa dea nec dignata cubili est,
Ecl. iv. 62. [*]( Those that have never smiled on their parents, neither does any god honour him by admitting him to his feats nor goddess deem him worthy of her bed." Although there can be no doubt as to the correctness of Politian's emendation in the passage as quoted here, it is against all MSS. authority, both of Virgil and Quintilian, and it is still frequently held that Virgil wrote cui. )
where
he whom no goddess deems,
etc., is included among
those who have never smiled,
etc.