Do you have the Latin?
Jack Cannon, a colleague in Cincinnati, used to be fond of quoting an old British comic routine: “I wanted to work in the mines, but I didn’t have the Latin.”
For a long time, going to school meant learning Latin. You didn’t study your own language at school—you knew that—you studied Latin because it was the prestige language, the language of learning, law, and the church, and because it was hard.
Even in the United States within living memory, it was commonplace for students in public high schools on the college-prep track to take two or more years of Latin. I did myself, and was, like the Belgae, defeated by Julius Caesar.
The enduring impact of Latin on English can be seen in words imported intact from that language: We still have alumnus, alumna, alumni, alumnae, though I expect that fairly few alumni have mastered the distinctions.
And we find faux-Latin coinages irresistible: Literati, the literary intelligentsia, inspired glitterati, the ostentatiously fashionable.
But, English being English, the language naturalizes and transforms some of what it adopts. It is perfectly all right to use memorandums, referendums, and forums. Memoranda, referenda, and fora are more than a little precious. Data, like it or not, is either a plural noun or a singular collective noun, depending on context.
And, people being people, you also get coinages from writers whose knowledge of the classical languages doesn’t extend beyond changing us to i to form plurals. That’s why you see octopi, though octopus comes from a Greek word rather than a Latin one, with the plural form octopodes.* If you’ve got more than one, you have octopuses.
I know that some of you are going to yearn for a Rule to guide you thorough this thicket, and, as always, I’m pleased to provide one:
English is English, except when it’s not.
I’ve said before that English is a magpie language, forever picking up shiny things. Some borrowings keep their original forms, but many more are transformed. There’s no rule. You have to learn the distinctions, case by case, which is why investing in a couple of good dictionaries is a smart move.
*Insist on using octopodes, and you have a fair chance of getting a star on the Pedants’ Walk of Fame.