Discussion Forum—A Way with Words, a fun radio show and podcast about language

By Jove! That is a good question. As is typical with English, it depends.

In specialized writing and speaking, such as academic treatments, where the audience is expected to know English and the source, there is a large likelihood of preserving the source language inflection, especially nominative plural, posessives, and gender markers.

For words and phrases in common use, the vast majority of words come in as nominative singular. Some preserve their source language nominative plural, but the majority take regular English plural and posessive forms. Phrases, especially fixed phrases, tend to preserve their inflection in the source language.

I will try to develop a good list of examples and add them in a bit. Of course, By Jove is one of the unusual exceptions where Jupiter is found in a prepositional oblique form even though it follows an English preposition!

On principle, I used to try to convince people to use “memoranda” (which this integral spell check tells me is misspelled) as opposed to “memorandums” (with which the spell check has no problem). As you might imagine, I was entirely unsuccessful.

It's not a perfect example, since it's not so much a direct import from another language accurately reflecting case, but as a nod to the original plural format, it's at least indicative of the general disregard for preserving the original grammatical format.

You may be pleased to learn that Magna opera still beats out Magnum opuses. Perhaps this is an indication that magnum opus is isolated to more academic circles.

Other interesting exceptional cases are Rebus / rebuses, omnibus / omnibuses.

Another oddball case study: paterfamilias. This has become a fused word, and yet most dictionaries list the plural as patresfamilias. Personally, I would probably use paterfamiliases without doing the research, assuming that such a word would be best understood than any fancy plural.

My limited Latin study made me curious about the -familias part, as opposed to -familiae, and I learned -familias is an archaic genitive singular. The archaic part made me smile since I am forced to suppose that means even more archaic than expected for a Latin genitive singular I learned in high school. So that explains why it is not *paterfamiliae. But then I would expect that patresfamiliarum would better express the plural of paterfamilias than does patresfamilias as the multiple heads are not lording over a single household. But who died and made me Caesar?

I found only one dictionary that lists paterfamiliases as a plural, and that one splits the plural between two senses, listing paterfamiliases for the generic sense, and reserves patresfamilias in the specific Roman sense.

The Google plebiscite overwhelmingly favors patresfamilias over paterfamiliases. Patresfamiliarum appears some in a Google search, if not in the dictionary, but at least some are Latin entries, so it is hard to count how many of them are using them as part of English writing.

The same could be true of patresfamilas but I didn't note any Latin entries. Could this be because it is indeed an unlikely plural used only for multiple heads of a single family?

Here is an entry in a Latin lexicon on steroids, Lewis & Short, that discusses familia, its old genitive familias and even the dual plurals patres familias / patres familiarum.

familia