Does it indicate a possessive adjective or just a plural noun? If noun, why it is not CPUs (without apostrophe)?

Windows CE 2.0 presentation: What CPU's will it run on?

  • 88
    Because inability to punctuate isn't a compile-time error in English. ;)
    – Wildcard
    Aug 3, 2016 at 0:01
  • 14
    You have discovered the Grocer's apostrophe - Google it and smile :-)
    – Mawg
    Aug 3, 2016 at 8:38
  • 9
    @Wildcard Actually, using an apostrophe in plurals of initialisms is considered correct by well-respected style guides. And it's always considered correct when pluralizing single letters ("Mind your p's and q's."). See choster's answer. Aug 3, 2016 at 10:32
  • 2
    Interesting. In Dutch we use the apostrophe the other way around - it's not there for the possessive ("Peters boek" instead of "Peters book") but we do use it for plural of nouns ending in a vowel ("baby's" instead of "babies"). Therefore a lot of native speakers have the tendency to form plurals in English with an apostrophe.
    – CompuChip
    Aug 5, 2016 at 8:15
  • 2
    @Mawg I think there needs to be a new name for cases when people call something a "grocer's apostrophe" when it's not one, as is the case here.
    – Jon Hanna
    Aug 5, 2016 at 10:28

5 Answers 5


It's one way of showing plurals that is used with acronyms.

It's widely-used, but whether it is correct is the subject of debate. It may be best to avoid its use in formal or professional documents. Generally, CPUs will always be considered valid, while CPU's may or may not be (this applies to other acronyms).

You may find these resources interesting:

  • 13
    Technically, CPU isn't an acronym ;)
    – Catija
    Aug 2, 2016 at 20:21
  • 20
    @Catija: I'm calling "common usage" on acronym vs initialism :)
    – LMS
    Aug 2, 2016 at 20:23
  • 13
    @Catija CPU isn't an acronym? It doesn't stand for "central processing unit"? That's what I learned some 30-odd years ago...
    – Doktor J
    Aug 3, 2016 at 5:53
  • 26
    @DoktorJ Technically the term acronym refers to initialisms that are pronounced as a word. Examples include NASA or scuba. If you say the letters individually, it is not an acronym.
    – Catija
    Aug 3, 2016 at 6:06
  • 19
    Blind prescriptivism makes me so frustrated! :P You cannot say "this is wrong" and "technically it means this" with language, it just doesn't work that way. You can say "according to X, it means this", or "based on logic Y it should be this", but there is no "perfect English" that exists somewhere that we are all trying to achieve. If 50% of the world said that "All TLA's are acronyms" is a valid and true English sentence, and the other 50% called it "wrong", there is no authority with the power to judge between them.
    – IMSoP
    Aug 3, 2016 at 13:42

Punctuation is a matter of style. Here, 's is almost certainly used to pluralize the initialism CPU, but whether this is appropriate depends on which style manual you, your editor, or your organization follows.

The New York Times stylebook, which is derived in large measure from Associated Press style, has this to say about plural abbreviations:

Use apostrophes for plurals of abbreviations that have capital letters and periods: M.D.’s, C.P.A.’s. Also use apostrophes for plurals formed from single letters: He received A’s and B’s on his report card. Mind your p’s and q’s.

But do not use apostrophes for plurals of abbreviations without periods, or for plurals formed from figures: TVs, PCs, DVDs; 1990s, 747s, size 7s.

In contrast, APA Style fully rejects any use of apostrophes to indicate plurals:

Just as with numbers, don’t include an apostrophe when pluralizing abbreviations. For example, when pluralizing an acronym, such as “CV” for “curriculum vitae,” all you need to do is add an s to the end, as in “CVs.” This rule also applies to standalone letters, as in “The students all received As.” For abbreviations that end with a period, such as “Ed.” to indicate an editor in a reference list entry, add an s before the period, as in “Eds.” When pluralizing an italicized abbreviation, remember not to italicize the s, as in “ps.” Just don’t add an apostrophe.

The Oxford Guide to Style (2002 edition of New Hart's Rules) offers similar guidance:

Do not use the apostrophe when creating plurals. This includes names, abbreviations (with or without fall points), numbers, and words not usually used as nouns: the Joneses · several Hail Marys … · B.Litt.s · QCs … · the three Rs … · sixes and sevens

The Chicago Manual of Style guidance states

Capital letters used as words, numerals used as nouns, and abbreviations usually form the plural by adding s. To aid comprehension, lowercase letters form the plural with an apostrophe and an s.

  • 4
    Wow! APA really wants "What's with all the maybes?" and "Your penmanship is good except for your is and ss."? Crazy. Aug 3, 2016 at 7:19
  • 9
    @DavidSchwartz: Personally I'm happy with your first example: if "maybe" is a noun that can be pluralised, then the plural is "maybes". But it could be fixed as "What's with all the "maybe"s?" The latter could be semi-fixed as "Is and Ss", or at a risk of sounding archaic, as "ies and esses". This is what happens when you make a prescriptive rule, they've painted themselves into some unpleasant corners. Aug 3, 2016 at 9:50
  • 3
    You should potentially add the Oxford Guide to Style as a UK English reference (showing that this isn't just an American choice to not use an apostrophe here): "Most abbreviations form the plural by adding -s: VIPs, MCs, SOSs"
    – Jules
    Aug 3, 2016 at 11:00
  • 3
    You provided references to four separate style guides, but none of them support the assertion that 's is acceptable in this case. The NY Times and Chicago style guides advocate its use with abbreviations that include periods, but CPU is not such an abbreviation, and their stance is that it should be "CPUs." I'm not saying there that it isn't a valid stylistic choice, but you should probably find an example to prove that it is before making the claim.
    – bcrist
    Aug 4, 2016 at 1:56
  • 2
    The form CPUs is increasingly not the more widely accepted and may completely replace that use of apostrophe, but not so long ago CPU's was the more widely accepted. I go into more detail on this on an ELU question at english.stackexchange.com/a/104235/15770
    – Jon Hanna
    Aug 5, 2016 at 10:33

There's a lot of argument about proper pluralization of acronyms and initialisms.

Both using and not using apostrophes is an acceptable method of pluralization (depending on what resource you use), so it's a matter of case-by-case interpretation to determine whether it's possessive or plural.

There's no way to interpret the sentence you have in your image as a possessive statement, though, so it is clearly being used as a plural form of CPU.


Because not using an apostrophe often looks ridiculous, it cannot be universally prohibited. Since it's not universally prohibited, it is sometimes allowed. For "CPU", some people prefer "CPU's" for the plural but most prefer "CPUs".

To see why you sometimes have to use an apostrophe to indicate a plural, try removing the apostrophes from the plurals in bold below.

"Your penmanship is good overall, but your S's and I's need more work."


"What's with all the maybe's?"

  • 3
    What is it with all the maybes? In other words, would you care to explain, why "maybe" is substantially different from any other noun placed in that position? If it's exactly because it's not a noun, what's your take on "do(')s and don'ts"?
    – LLlAMnYP
    Aug 3, 2016 at 8:54
  • 2
    "it reads like it should be pronounced" - This valiant effort notwithstanding, the ship has sailed on words in English that don't read how they're pronounced ;-) Aug 3, 2016 at 9:54
  • 3
    @SteveJessop make no mistake, "maybes" should be pronounced may-bees and that's exactly how it reads :-)
    – LLlAMnYP
    Aug 3, 2016 at 9:55
  • 1
    The way to make it clear is to use the tool that's traditionally used when referring to a part of some other text: quotes. What's with all the "maybe"s? and your "S"s and "I"s need more work.
    – Blorgbeard
    Aug 3, 2016 at 20:36
  • 1
    Well, I didn't get that impression from your text with apostrophes, so it seems they're not really doing the job either.. And I doubt you were referring to general s-shaped things, considering "penmanship". Can you come up with an example that doesn't involve a noun that's not usually a noun?
    – Blorgbeard
    Aug 3, 2016 at 21:04

Whatever the New York Times may say about it, why should one use the apostrophe as an additional sign for plural? 's is indicative of the Saxon genitive.

My best advice is: keep 's for the Saxon genitive and regard other usages as a common mistake (yes: mistake). In that case: What CPUs will it run on?

Incidentally, the quoted piece of reference is stale —PowerPC was outphased more than a decennium ago.

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