PI's? PIs? POs?

I thought I'd tackle a simple editing question today. This was spurred by an article in the Chronicle of Higher Education on "Is 'Mens' Becoming a Word?'" In this article, the author notes how he is starting to see signs and uses of the word "mens" as possessive without an apostrophe. He seems open to our evolving language, usage, and grammar, but the word mens does not sit well with him.

This got me thinking about apostrophes or lack thereof that never sit well with me, and the first thing that came to mind was when I'm using the abbreviation for Principal Investigators in the plural. When I write PIs as plural, I have an urge to include an apostrophe: PI's. Why? Why do I want to do that when I'm not using the possessive? Well, it's because of other uses that I am comfortable with that use an apostrophe for the plural, non-possessive. Phrases like, the 90's or the ABC's. Neither of these phrases are necessarily possessive, but many of us are comfortable with the apostrophe in these cases, right? However, as shown in the APA blog below, we probably shouldn't be using apostrophes in the 90s or the ABCs.

OK, so I won't drag it out any further. The thing to do when you aren't quite sure which way to go or get that uneasy feeling when you make a grammatical decision, is to go to the authority. Who is the authority, you ask? Is it APA, MLA, Chicago, or Turbian? No, in this case the authority is the agency to which you're applying. If you're writing for the NIH or the NSF, go use the search engine on their site to see what grammatical rules they're using, and follow their lead. If you're wondering, like I was, about possibly including an apostrophe in the possessive form of PIs, a quick search tells us. No, neither the NIH nor the NSF include an apostrophe - it's PIs and POs.

Whew, glad I sorted that out! :)

Resources:
Is 'Mens' Becoming a Word? - Ben Yagoda, Chronicle of Higher Education
Pluralize Numbers and Abbreviations Without Apostrophes - David Becker, APA Style