Abbreviations, initialisms and acronyms

We've been a little self-indulgent and playful during the holiday season, but readers are calling us back to business. Here's one:

For many years I have had anxiety about the plurals of acronyms and initialisms. I have no idea what the correct form is. I find myself typing PC's sometimes to mean more than one PC. I see others do it too. The apostrophe seems wrong because PC's is not a contraction nor does it imply possession. PCs looks a little weird and if it needs to be capitalized PCS would simply be incorrect at times.


Let me try to put those anxieties at rest. The problem is not one of choosing between correct and incorrect forms, but of choosing from a set of options and following the choices consistently.

An abbreviation like PC can be made plural as either PCs or PC's. The Associated Press Stylebook and The Chicago Manual of Style recommend the former, The New York Times the latter.


Now let's make it more complicated. If, however, an abbreviation contains internal periods, Chicago joins New York Times in wanting you to include an apostrophe: M.A.'s and Ph.D.'s. And The Times uses periods in abbreviations — C.I.A., F.B.I. — when AP and others do not.

Everyone encourages you to use an apostrophe when making single letters plural: all A's, p's and q's.

Abbreviating names leads to two categories, initialisms and acronyms. An initialism uses the first letters of the words being abbreviated and is pronounced letter by letter rather than as a word: FBI, mph. An acronym combines first letters or compounds of the constituent words into an abbreviation that is pronounced as a word: NASA, scuba. If it's not pronounced as a word, it's not an acronym.

Initialisms may or may not include periods; acronyms do not. Initialisms may be written as capital letters or lowercase letters. Acronyms tend to be written all caps — UNESCO — though some prefer to write acronyms of five or more letters with an initial capital followed by lowercase letters. But the latter practice tends not to be followed uniformly.

The definite article is used before abbreviations of agencies — the FBI, the CIA — and nations — the U.S., the U.K. — but not before the abbreviations of universities' names. Devoutly as some might wish, Ohio State University is not called the OSU. Some bureaucrats indulge in omitting the article before the names of their agencies, because they are very important people, pressed for time on the nation's business and too urgently focused on the public weal to trifle with the definite article. For them, it's OMB says and EPA reports. But if you were interested in mimicking pomposity, you wouldn't be reading this.

What it comes down to, as is so often the case, is that you have a range of acceptable choices. Pick the one that is consistent with your personal preference and the practices of the publication you write for, and stick with it.

It might not amuse you to consult AP or Chicago or some other manual to see just how complicated they can make things, but otherwise, be not afraid.