Looking back on earlier Pet Peeves, I mentioned the its vs it’s issue. Well, it is time to return to a discussion on apostrophe usage that can be very confusing and frustrating. In multiple books I have proofread recently, I have struggled with the poorly defined rule of s or ’s to pluralize an acronym or initialism. Do you add an s, ’s or can the word be plural without adding anything?

We can all agree Automated Teller Machine would be ATM or A.T.M. as an acronym.
But what about Automated Teller Machines? ATM, ATMs, ATM’s or A.T.M.’s?

ATM alone makes you always think singular so it feels like you need the s somewhere. ATM’s looks like it is possessive and not plural. A.T.M.s just looks strange.

The Chicago Manual of Style has a hybrid view of this issue omitting the apostrophe, unless there are periods in the abbreviation. So for an automated teller machine, this would give you ATMs, or alternately A.T.M.’s

The AP Stylebook does not appear to have a specific ruling on pluralizing acronyms but it does have sections where single letters use the apostrophe to pluralize them such as A’s, B’s, C’s. So nothing definitive there.

Some references I have found in my research say if the acronym ends in an S, like SOS, then you have to use the apostrophe as in SOS’s. But then how would you manage the plural possessive form? Would it be SOS’s’s?

How about in games?

Hit Point = hp or HP
Hit Points = hps? HPs? hp’s? HP’s? Or just HP as plural and singular? “Reduce his HP by D6.” or “Reduce his HPs by D6?” I have seen both standards utilized in books.

As an editor and proofreader, I look to the style guides utilized by the publisher. What is their standard? If they have not set a standard, discuss with the publisher and be consistent throughout the book and game line. For something like this that does not have a definitive industry standard, what often is best is what reads the smoothest.

How do you handle plural acronyms in works you edit or proofread?

Proofreader Pet Peeves List #5

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