All Mavens: alert! The plural of jackknife, a move made in diving and workouts, is jackknifes, but you Mavens must set us straight and remind us that knife has an irregular plural, knives, so it must be jackknives. I searched several on-line dictionaries and found only one instance of the plural when it did not mean an actual knife and it gave “jackknives”; however, I sensed that the citation was not a quote but made up by the dictionary compiler. Neither my American Heritage or Webster’s New Collegiate give the plural of jackknife in the 90 degree sense.
I suspect that if you were to hang out at the pool or walk through the gym, you would hear, “How many jackknifes did you do?” The reason is that a 90 degree jackknife, whether by a person or a tractor-trailer rig, is not a knife. Steven Pinker devotes a lot of attention to this phenomenon because it demonstrates how the brain stores language features like plurality. The normal s plural gets put on a word as it comes out of its lexical slot in the brain. But irregular plurals, like knife~knives, mouse~ mice, tooth~teeth, etc. cannot be treated that way and are stored as separate lexical items, i.e. the process, if I understand Pinker correctly, by which you pull the word â€˜sandwich’ out of your brain is the same one you use to pull out â€˜knives’ or â€˜feet’, which have their own slot just as â€˜knife’ or â€˜foot’ do. That’s why we don’t say, “In caveman days the saber tooth tiger was a real danger and there were a lot of *saber teeth around then”………. we say “a lot of saber tooths around….” The Canadian hockey team is known as the Toronto Maple Leafs, not Maple Leaves, b/c they are not really leaves.
More examples can be found. I’d like to know the plural of â€˜mouse’ when the mouse is attached to a computer. Merriam-Webster on-line says the plural for the device can also be â€˜mouses’; I believe a lot of English teachers insisted on â€˜mice’, so people are conflicted.
A fascinating case of confliction is offered by Pinker with the plural of Walkman. For those under 30, the Walkman is a device that plays the radio or a tape and is listened to via headphones. It is called a Walkman b/c the idea of it was for people to be able to listen while walking. But the plural has always been in doubt: Walkmans or Walkmen? (My spell checker likes neither). Unlike all the other cases where the plural is clear-cut except where school marms intervened, this word refuses to be resolved to anyone’s satisfaction. The answer why not (like that, Mavens?) comes out of a hint: the Walkman was made and named by people whose native language is not English. That’s right, the Japanese made an English compound word that violates the way English forms compounds, i.e. the head word is unclear: is it â€˜walk’ or â€˜man’? Even used metaphorically, an irregular noun keeps its irregular plural, as in â€˜the saw teeth of the blade’. But in the case of walkman, it is a headless compound, shown by the fact that heads are on the right and yet a Walkman is not a man, so the headword on-the-right rule doesn’t work here. There is no clear relation between â€˜walk’ and â€˜man’ in this compound and so we can’t get a fix, according to the rules of English compounding, on what the plural should be. The reason for THAT is b/c it is one of those bizarre concoctions Pinker cites Circuit Beaver, Nurse Mentality, and the like seen on Japanese T-shirts; English is just popular, not necessarily well-known.
Should you wish to read more on this topic which should sink any Maven’s aspirations to tell us all the rules of English, read The Language Instinct by Pinker. pp. 141-147. Oh, and if you are a Maven and dismiss all this as so much empty linguistic theorizing, display your high culture by referring to the “still lives” you bought at the art show and listen to people ask what country you’re from.