Q. I’m proofreading a manuscript in which a lot of dialogue tags are followed with descriptive verb phrases. But instead of using gerunds to do this (“I like cats,” he said, smiling), the author opts nine times out of ten to use a conjunction (“I like cats,” he said and smiled). In most of these cases, my instinct is to put a comma after the dialogue tag, but I’m unable to find any CMOS rule that applies to this specific instance.
A. A comma in your second example isn’t strictly required; the word “and” introduces the second half of a compound predicate (“smiled”), which is easier to see if you reorganize your example and replace the quoted dialogue with an indefinite pronoun:
He said something and smiled.
But the transition from speaking verb (“said”) to action verb (“smiled”) in the original version of the example is a little abrupt, and we agree with your instinct that a comma after “said” would be helpful:
“I like cats,” he said, and smiled.
For a similar take on this issue, see Amy J. Schneider’s The Chicago Guide to Copyediting Fiction (University of Chicago Press, 2023), 163–64. See also CMOS 6.24 (on commas with compound predicates) and 12.41 (on punctuation with speaker tags).