There are hidden rules not just in grammar, but at every level of language production. Take pronunciation. The –s that marks a plural in English is pronounced differently depending on the previous consonants: if the consonant is “voiced” (ie, the vocal cords vibrate, as in “v”, “g” and “d”), then the –s is pronounced like a “z”. If the consonant is “unvoiced” (like “f”, “k” and “t”), then the –s is simply pronounced as an “s”. Every native English-speaker uses this rule every day. Children master it by three or four. But nobody is ever taught it, and almost nobody knows they know it.
From the Economist: Hidden in plain sight.
I am fascinated by linguistics. It never existed in my mind as a subject before I read some Chomsky, and yet I find it fascinating. See the papers in last week’s Nature about human genetic diversity and our history, and linguistic diversity in Australia (there is an article about this in Science).
But one reason why the above amuses and intrigues me, is that it is clear in so many clinical situations that we know more than we can say. We really are very poor at explaining clinical competence, and until we think hard about this issue, our teaching remains worse than it might be.