Specifically, I’m talking about the difference between “was” and “were” in sentences like these. “Was” suggests it’s possible the burglar had a good head on his shoulders. “Were” suggests he did not.

Any native speaker can pick up on that. But if you asked 100 of them to explain what’s going on with those two verbs, somewhere between 99 and 100 would have no idea.

And if they spent all day reading dictionary definitions they would be no closer to understanding the basis of these different meanings of “was” and “were.”

To understand them from an academic perspective, you need to start with a single word: subjunctive. That’s the grammar term that describes what’s going on here. And I explain it in full in my recent column.