Q. I’m confused why there is a comma before “as well as” in CMOS 6.19: “The team fielded one Mazda, two Corvettes, and three Bugattis, as well as a battered Plymouth Belvedere.” If “as well as” was replaced with “and,” there would not be a comma. I can’t find anything else about this in the Manual. Can you please explain?

A. The comma tells us to read the Belvedere as an afterthought—it hints that the battered car is in a different league from the other cars. A search of the Manual for the phrase “as well as” reveals that it is sometimes introduced by a comma and sometimes not, depending on context and meaning.