Institutio Oratoria

Do not nouns which are similar in the nominative show, as I have already observed, quite different terminations in the oblique eases? Compare uirgo and Iuno, lusus and fusus, caspis and puppis and a thousand others. Again some nouns are not used in the plural, while others are not used in the singular, some are indeclinable, while others, like Jupiter, in the oblique cases entirely abandon the form of the nominative.

The same is true of verbs: for instance fero disappears in the perfect and subsequent tenses. Nor does it matter greatly whether such forms are nonexistent or too harsh to use. For what is the genitive singular of progenies or the genitive plural of spes? Or how will quire and ruere form a perfect passive or passive participles.