Apostrophes for the Plurals of Abbreviations and Awkward Plurals

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The Quick Answer
If you have an awkward plural (usually the plural of a letter, a number, or an unusual abbreviation), you can use an apostrophe to assist your readers. For example:
  • Hawaii is spelt with two i's.
  • She used six and's in one sentence.
Beware! This is not a popular practice (even though all the modern grammar references condone it).
apostrophes for the plurals of abbreviations
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Apostrophes to Show the Plurals of Abbreviations and Awkward Plurals

The first thing to make clear is that apostrophes are not normally used for forming plurals. (This is covered more in the lesson Apostrophe Errors with Plurals.)

In other words, using an apostrophe to form a plural is usually a grammatical mistake. For example:
  • She will not eat banana's.
  • Is it true that pearl's melt in vinegar?
However, sometimes, a plural is so awkward, it is permissible to use an apostrophe to assist your readers. For example:
  • There are two a's in accommodation.
  • Your 2's look like your 7's.

Assist your Reader

The advantage of using an apostrophe is that the abbreviation, letter, or number is instantly recognizable. However, when an apostrophe is used to show a plural, it could lead to ambiguity because apostrophes are mostly used to show possession (e.g., the dog's bone) or in contractions (e.g., the dog's eaten the bone). Look at these examples:
  • MP's Plan Failure
    • (This newspaper heading is ambiguous. We cannot be sure if the apostrophe shows a plural (the journalist's intent) or possession. Is this title about (1) MPs planning to fail? or (2) the failure of an MP's plan? It's unclear.)
  • The MP's leaving are to be replaced by Monday.
    • (In this example, the apostrophe shows a plural. This is likely to cause a reading stutter. Upon reading the sentence, most readers would see "MP's" as a possessive, and some would see it as a contraction of "MP is." Only when readers reached "are" would they realize it was a plural. Of course, the apostrophes in both of these examples are unjustified because "MPs" is not an awkward plural.)
So, remember that using 's to show a plural can lead to ambiguity. Even if there is no real ambiguity, it will at least make the reader pause momentarily to check whether the apostrophe shows a plural, a possessive noun, or even a contraction. In other words, your plural apostrophe is likely to cause a reading stutter.

You should only use an apostrophe in the plural of an abbreviation, a letter, or a number to assist your reader.

Examples of Apostrophes Showing Plurals

Here are some acceptable examples featuring apostrophes for plurals.
  • You use too many and's in your writing.
    • (The apostrophe assists the reader in this example.)
  • There are two consecutive i's in the words skiing and taxiing.
    • (The apostrophe assists the reader in this example.)

Apostrophes in Plurals for Uppercase-Only Titles

When writing titles, you are sometimes compelled to use just capital letters. This makes it difficult to show a plural of an otherwise normal-looking abbreviation. Remember that if it assists your reader, you can use an apostrophe to show a plural. For example:
  • CD'S ARE OBSOLETE
  • TWO LRS'S PER PROCESSOR

Do not Use an Apostrophe for the Plural of a Normal Abbreviation

It is worth reiterating this point. Do not use apostrophes for the plurals of normal abbreviations. For example:
  • He had 4 CCJ's against him.
  • He had 4 CCJs against him.
    • (Note: CCJ = County Court Judgment)

  • M.O.T.'s
  • M.O.T.s
    • (Note: MOT = Ministry of Transport / also Ministry of Transport test)

  • MOT's
  • MOTs
Note: It is often the writer's choice whether to use periods (full stops) in abbreviations.

Do Not Try Too Hard to Avoid the Apostrophe

Of course, there are other ways to show an awkward plural. For example:
  • Hawaii is spelt with two "i"s.
  • Hawaii is spelt with two Is.
  • She used six ANDs in one sentence.
  • She used six ands in one sentence.
These methods are acceptable, but the apostrophe version is usually far neater and clearer.

Key Point

Some grammar pedants claim that apostrophes cannot be used in any plurals. This is an outdated, dogmatic view. However, using an apostrophe for a plural is still an unpopular convention, and it could irk some of your readers. Therefore, you should try to avoid it.

The ruling, however, is that you can use 's to show an awkward plural. So, if you have an awkward abbreviation, number, or letter and adding 's gives you the best-looking plural, go for it.
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See Also

Using apostrophes The apostrophe error with plurals Apostrophes in time (temporal) expressions Apostrophes replace letters Apostrophes show possession Full stops (periods) in abbreviations "Apostrophes for possession" game (Tetris-style game) "Apostrophes in time expressions" game (Tetris-style game)