Commas

Q. Hi, Chicago—I’m replying to your e-mail answer more than seven years later because I’m still trying to wrap my head around punctuating sentences like these:

She was still so shocked, it took her a while to find her voice.

He was so fixated on his game, he had no idea I’d entered the room.

Do they require the comma? Based on your seven-year-old e-mail reply (“I don’t know of any such rule”), I’ve been deleting most such commas. Occasionally, I’ll replace the comma with a semicolon. But I guess what I’d like to know now is this: Is there any rule (preferably somewhere I can cite) that governs this type of sentence?

A. I’m happy to report that after seven years of intensive focus on your question, the CMOS team has still not encountered a rule for this. Please note that when it’s this hard to find a rule, it’s likely that nobody knows one or cares. We hope this helps you move on. If not, please write again in 2020.