When it is acceptable to use one of *those* apostrophes

It seems that everyone is an apostrophe nazi these days – either that or absolutely terrified of using one incorrectly and subsequently being exposed as a dunce.

I don’t mind – I’m a fully paid-up apostrophe nazi, and not ashamed to admit it, and it forms a part of what I do of a living. But, it really irritates me that many people, many educated people, don’t realise that there are certain (at first glance wrong) apostrophes that are quite correct.

These people should mind their p’s and q’s.

Did you see what I did there? I exposed myself as a massive idiot didn’t I. Please feel free to pelt me with rotten fruit and seduce my wife.

But wait, allow me to retort. It is quite acceptable to use an apostrophe when referring to plurals of letters. Not all style guides agree on this, and not all style guides agree on whether is it is acceptable to use one when referring to plurals of capital/lower case letters. It isn’t black and white, but it certainly isn’t the apostrocrime many people think it is. I’m bored of arguing about this on Twitter, and having to re-research it each time, so I’ll list a few examples below.

First off, and perhaps most accessibly, Eats Shoots & Leaves by Lynne Truss has this to say:

It indicates plurals of letters:
How many f’s are there in Fulham? (Larky answer, beloved of football fans: there’s only one f in Fulham)
In the winter months, his R’s blew off (old Peter Cook and Dudley Moore joke, explaining the mysterious zoo sign “T OPICAL FISH, THIS WAY”)

I’ll pick the bones out of that for you: The plural of f is f’s and the plural of R is R’s.

Oddly enough, my go-to style guide, the Guardian Style Guide doesn’t mention the apostrophe’s role in plural letters – not online anyway. If anyone has the print version, could they let me know in the comments if it does.

The next few examples are drawn from this forum post. This saves me hours of research, and as it contains references to both schools of thought I have no reason to question its accuracy.

IBM Style Guide:

Form the plural of a single character (except 0, 1, M, and the vowels a, e, i, o, u, A, E, I, O, and U) by adding s alone. Adding s alone to form the plural of these exceptions produces combinations that couldbe confused with words or common abbreviations (Is, as, Ms, and us). Because of this, the plurals of 0 and 1 should be either spelled out as zeros and ones, or formed by adding an apostrophe and an s (0’s and 1’s). The plurals of a, e, i, o, u, A, E, I, M, O, and U should be formed by adding an apostrophe andan s (a’s, e’s, M’s, and so on).

Perdue University:

To form the plural of a lowercase letter, place ‘s after the letter. There is no need for apostrophes indicating a plural on capitalized letters, numbers, and symbols

University of Sussex:

An apostrophe is indispensable, however, in the rare case in which you need to pluralize a letter of the alphabet or some other unusual form which would become unrecognizable with a plural ending stuck on it

University of Delaware:

[Use an apostrophe f]or Pluralizing Letters, Numbers, Symbols, and Words Used as Terms.

CCCF Guide to Grammar and Writing:

An apostrophe is also used to form some plurals, especially the plural of letters and digits. Raoul got four A’s last term and his sister got four 6’s in the ice-skating competition. This is particularly useful when the letter being pluralized is in the lower case: “minding one’s p’s and q’s” or “Don’t forget to dot your i’s.” (In a context in which the plural is clear, apostrophes after upper-case letters are not necessary: “He got four As, two Bs, and three Cs.”)

As most of those are for American English, I thought I’d finish with the Oxford University Press style guide:

There are one or two cases in which it is acceptable to use an apostrophe to form a plural, purely for the sake of clarity: [Y]ou can use an apostrophe to show the plurals of single letters [and Y]ou can use an apostrophe to show the plurals of single numbers

So there you go (and I’m impressed that you have read to the end of this) it is, in some cases, and in some style guides and under certain circumstances acceptable to use one of those apostrophes.

What do you think?