By Grammar Girl
The World Series has fans asking how to make an abbreviation such as RBI plural. It can be confusing, since it’s the R-part (run) that is becoming plural. Should it be RsBI or RBIs or something else?
Even though it doesn’t make absolute logical sense, you make initialisms and acronyms plural by adding an s to the end no matter what part would be plural if you wrote the whole thing out: even though it would be runs batted in, you write it RBIs.
Can You Ever Use an Apostrophe?
In the past, some publications used apostrophes to make acronyms and abbreviations plural, so until a few years ago, it was common to see something like RBI’s or CD’s in the New York Times. Currently, all major publications and style guides I’m aware of recommend simply adding an s (without an apostrophe).
When Do You Use Periods?
Whether you put periods after the letters in an acronym such as NASA or an initialism such as RBI is a style choice. Some publications do and some publications don’t.
Mignon Fogarty is the author of 101 WORDS TO SOUND SMART. Find out how to get free wallpapers when you preorder the book before November 7, 2011.