Besides, a dodgy discourse marker

I’ve just been giving feedback on a piece of writing by a non-native speaker and came across a common misuse of the word besides in a sentence initial position as a discourse marker/linker. The writer has used it to add another point, in a fairly neutral way, as you might use ‘and’ or ‘also’, or perhaps ‘in addition’.  

“I work at a language institute […] Besides, I tutor business students one-to-one.”
(that’s a paraphrase, but it keeps the sense)

It’s a usage I’ve come across countless times in students’ essays and one I always flag up or correct, but generally avoiding commenting on because it’s tricky to put your finger on exactly what’s wrong about it. If you look in a learner’s dictionary, you’ll find a rather neutral definition like “in addition to; also” and sometimes a note which hints at something more:

Macmillan Dictionary: used when you are adding another stronger reason to support what you are saying

Collins COBUILD: Besides is used to emphasize an additional point that you are making, especially one that you consider to be important

OALD: The adverb besides is mainly used to give another reason or argument for something

I don’t think any of them really get to the heart of how this seemingly simple little word is actually used though. That’s not to criticize the dictionaries, which are only trying to be as concise as possible and do show more using examples, but there’s just quite a lot going on. After a bit of thought and looking at quite a few examples, I think you use besides when you’re trying to make an argument, you’ve set out some points, then you want to introduce your final trump card. The besides means something like, “even if you weren’t convinced by everything I’ve just said, this last point trumps all of those and means I win hands down”.

A few corpus examples:
Shelly gave up looking for work. She said that she had too many projects of her own to concentrate on, and besides, she just wasn't "the office type." [COCA]

Your shoes are clean and neat. That is all that matters. Besides, we can't afford [new ones]. [COCA]

After a while, they stopped. There didn't seem much point in continuing. Besides, they were out of breath. [BNC]

I just thought you had enough to be getting on with, what with Jennifer. I didn't want to add to the problems. Besides, there wasn't anything you could do. [BNC]

As I looked through more examples, I also started to get the sense that this usage is fairly conversational, or at least used in writing that’s conversational in style. That led me to take a look at a more formal genre; academic writing in the BAWE corpus (of university student writing). At first I was a bit surprised to find quite a few examples of sentence initial Besides, … . But then when I delved further, I found that the majority of the examples (89%) were from non-native speaker writers, largely with Chinese L1 (that compares with something like 70% native-speaker scripts within the BAWE corpus as a whole). Although they were good writers of English, with good grades for their assignments, the usage still stood out as slightly marked. Perhaps an indication that, like me, no one could ever quite put their finger on what was odd about the usage, so had never corrected it for these writers.

Especially for new academic writers, discourse markers are a real minefield. We’re always telling EAP students how important they are to link their ideas together, but then when they choose the wrong ones, they jar and almost have the opposite effect on the reader (raising doubts about the logic of the ideas they link). I hope that in future, this is one pitfall that I’ll be better at proactively steering my students around.

PS Of course, all this ignores the apparently very similar, but actually very different usage: besides (preposition) + object, but that’s a topic for another day …