A great many common abbreviations* behave perfectly well in any fiction or nonfiction context, including dialogue, when the general guidelines in CMOS are observed: Mr., Ms., CEO, p.m., PhD, UFO. Editors should have no quarrel with them, as long as they’re styled consistently. If it’s 11:00 a.m. in chapter 1, it shouldn’t be 2 PM in chapter 3. That’s what style sheets are for.
Nonfiction versus Fiction
On the other hand, some of Chicago’s advice for wrangling abbreviations (see CMOS 10.3) can be safely ignored by fiction writers and editors. In a novel or short story,
