Originally posted on amastyleinsider:
Sometimes we see things out of the corner of our eye. Then we think, “Did I really see that?” Lately, I’ve had that experience with certain acronyms morphing from all capital letters (eg, UNESCO) to initial capital letters (Unesco).
When acronyms drop their periods, I take it in without a second thought—it looks cleaner to me, someone used to the omission of periods in most acronyms from years of editing using the AMA Manual of Style. But this move from all-caps to only an initial cap jarred me, once I stopped and looked it in the eye. I was puzzled, too, by the pattern (or lack of one) behind this shift.
A little investigation seemed in order. The AMA Manual of Style distinguishes between acronyms and initialisms1 and indicates that periods are usually not used with them. But there is no mention of an all-cap or initial-cap style or preference. The Chicago Manual of Style2 notes that “Usage rather than logic determines whether abbreviations other than those standing for proper names are given in upper- or lowercase letters. Noun forms are usually uppercase (HIV, VP), adverbial forms lowercase (rpm, mpg). Note also that acronyms, especially those of five or more letters, tend to become lowercase with frequent use (NAFTA/Nafta, WASP/Wasp).” Special mention of this morph is made in discussing associations and the like: “Whether acronyms or initialisms…, such abbreviations appear in full capitals and without periods. Acronyms of five letters or more may be spelled with only an initial capital….” Chicago cites ERISA/Erisa (Employment Retirement Income Security Act) as an example.