Knives redux

I love this example I came up with based on Steven Pinker’s Language Instinct examples of irregular plurals demonstrating the way we get a window into the brain’s workings via grammar. He used words like “tooth” “teeth” but “sabertooth” “sabertooths” to demonstrate that if the word does not denote what the head word is, “tooth” in this case, then it is not treated as an irregular plural, i.e. a “sabertooth” is not a tooth but an animal. What happens, apparently, in the brain is that the pathway for making words plural in a regular way is to select the word from storage, bring it to the platform where grammar is applied, and attach -s. But an irregular plural like “teeth” is stored just like any other word, right alongside “tooth” in this case. So it bypasses the grammatical stage as long as it is teeth we are talking about.
So I was reading my exercise book and noticed the name for one exercise is “jackknife”. “So how many jackknifes should you do?” “Wait a minute,” I thought, ‘jackknifes’? Why not ‘jackknives’?” Ah! A jackknife is not a knife, it is an exercise, therefore “jackknife” does not bypass the grammatical platform where the -s is added but instead does stop to take on the -s for plural.
This particular word demonstrates this nicely b/c there are so many words, like “penknife”, that denote an actual knife and so take the -ves plural: penknives. But even better, there is a knife called a jackknife, when the name for the exercise, which also uses the irregular plural: jackknives.
You can imagine a tough challenging a guy like this: “I have several jackknives on me and I’ll cut you if you don’t do 10 jackknifes for me.” Tough workout.

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