The Two Things about Linguistics:The first point is about tacit knowledge. In hearing Steve’s example about the speech of children, a critic might say that adults can articulate the rules of English grammar. But that is false; even accomplished native speakers cannot state everything there is to know. One thing I’ve found surprising about Neal’s work in linguistics (which I assume is fairly typical of the discipline) is how much of it involves trying to reconstruct mostly unrecognized, but nonetheless operative, rules of syntax. He does so by studying the actual utterances of speakers and writers who are speaking English without necessarily even thinking about it, and then trying to find underlying principles that describes all or most of them.
1. You already know more about the grammar of your native language than could ever be taught in a class. (synchronic linguistics)
2. Language change is inevitable, and neither bad nor good. (diachronic linguistics)
(Incidentally, I have taken issue with Neal’s item #2, on diachronic linguistics, here.)