Why everyone who works with language needs linguistics

Someone on a blog I read the other day posted this question, asking for advice:

Does anyone know any tricks to know when English -ed is pronounced as [d~t] as in “begged” and “knocked” versus [ed] like “petted”?

Some of my students have issues and I don’t know how to help them.

(I haven't linked to the actual blog because I don't want to seem like I'm criticising them personally.)

You might think that people who teach language know linguistics. Most people seem to think that linguistics *is* teaching languages. In fact, lots of linguistics graduates go on to do language teaching, but they are far outnumbered by language teachers who don't have a linguistics background. TESOL MA programmes frequently have a core linguistics component, but people who've chosen to do TESOL but not linguistics are probably not that interested in linguistics anyway.

The reason I mention this is that the question above is taught on any first-year linguistics course as the absolute go-to example of phonologically-conditioned allomorphy in English. Typically, we point out that native English speakers do this subconsciously and consistently, and it's an example of how there are rules and we can discover them by careful investigation, as well as to teach the theoretical concept.

Of course, speakers of other languages with different rules will not do this subconsciously, because the rules of their language might not automatically force the same result as English. They'll need the rule taught to them. The fact that someone who (presumably) is teaching English doesn't know how to explain this simple fact is quite shocking to me, but I doubt the asker is alone. A few basic linguistics classes would make life as an English teacher so much easier, I can't even imagine why it wouldn't be standard.

I just said no to some work

This is possibly a world first. I find it hard to turn down work, because the twin draws of money and experience are irresistible to me, and I feel like I'm letting people down. But today I turned down teaching work that was not only amazing experience (teaching on a TESOL MA course) but worth around £1400. That's a heck of a lot when you're in the last (unfunded) year of a PhD with no savings.

I would have loved to do the MA teaching (there was also some other teaching that was more appealing for the money than for the experience, though it would have been another string to my bow - discourse analysis, which I'm not sure what it is, and I don't think it's real linguistics, but apparently it's a thing), but it was just too much work. It was the phonology component of a linguistic theory module on the TESOL MA. I'm not a phonologist by a long chalk, but I've been teaching quite a bit of it so I can get by. But for an MA course, that's quite a lot of preparation, which eats into the (generous) hourly rate. Then there's the assignment, which requires them to transcribe their own speech. That means that I have to teach them phonetics as well as phonology (even more not my thing) and also, marking it means checking their transcription. This is a thing that takes a Long Time. So, regrettably, I said no.

But on the up side, that means I have more time for thesis-writing. And I've still got some teaching, just not that teaching.