Abbreviations
Q. I'm working with an author who insists that the proper typesetting of the abbreviations a.m. and p.m. is to set them in small caps and separate the letters with periods. Citing CMOS, I indicated that the author was incorrect because it says that if these abbreviations are set in small capitals, then periods are unnecessary. However, when I showed the author that section in CMOS, she pointed out that in the second example provided to show proper use with words such as “morning” or “afternoon,” 11:00 P.M. is shown with both small caps and periods. Is there an exception to the rule that is being exhibited in this instance? Any light you can shed on this seeming discrepancy would be appreciated.
A. Certainly: when CMOS says that something is “unnecessary,” it doesn't mean that it's wrong; it means that it's an option that's not our preference.
