Q. I recently became aware that many sources insist one absolutely must use a comma after “said” to punctuate sentences like this one: She looked up and said, “Hi.” Is this really a universal rule? The more I look into it, the more I feel I’ve slipped into an alternate universe.
A. According to CMOS 13.40, common one-word utterances can usually be introduced without the help of a comma—and without quotation marks or an initial capital:
She looked up and said hi.
We told her no.
Don’t ask me why.
But when such words are presented as direct discourse—as in the dialogue of a novel or story—they are usually placed in quotation marks and set off by a comma, like any other quoted words of dialogue:
She looked up and said, “Hi.”
“Hi,” I replied, a little embarrassed by the echo.
This convention suggests that the word or words in quotation marks were literally spoken as written. But it can be awkward to put the speaker ahead of the quotation. To smooth things out, try reversing the order:
“Hi,” she said, looking up.
For some additional considerations, see “Is a Comma Needed to Introduce Dialogue” in Fiction+ at CMOS Shop Talk.