Institutio Oratoria

I would suggest that the ripe scholar, who says

ave

His way is the right way. Who doubts it? But there is an easier and more frequented path close by. There is, however, nothing which annoys me more than their habit not merely of inferring the nominative from the oblique cases, but of actually altering it. For instance in ebur and robur, the forms regularly used both in writing and speech by the best authors, these gentlemen change their second syllable to o, because their genitives are roboris and eboris, and because sulpur and guttur keep the u in the genitive. So too femur and iecur give rise to similar controversy.

Their proceedings are just as arbitrary as if they were to substitute an o in the genitives of sulpur and guttur on the analogy of eboris and roboris. Thus Antonius Gnipho while admitting robur, ebur and even marmur to be correct, would have their plurals to be ebura, robura and marnura.

If they would only pay attention to the affinities existing between letters, they would realize that robur makes its genitive roboris in precisely the same way that limes, miles, iudex and uindex make their genitives militis, limitis, iudicis and uindicis, not to mention other words to which I have already referred.

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.