The apostrophe is one of the few areas of English grammar and punctuation where the rules are pretty simple and consistent, but every time I go shopping it’s clear that a lot of people struggle with its use.

The apostrophe does three jobs:

  • replaces a missing letter
  • shows possession
  • is used in special plurals such as abbreviations and single letters

Replacing a missing letter

Here the apostrophe is used to show that a letter is missing:

do not > don’t
will not > won’t
did not > didn’t
cannot > can’t
should not > shouldn’t
it is > it’s
who is > who’s
who has > who’s

Showing possession

Here the apostrophe is used before an s to show possession. For grammar junkies this is known as the genitive case.  Think of the ‘s here as a single unit:

The cat’s whiskers
Christine’s shoes
Shah’s coat
The house’s garden [one house]
The houses’ gardens [2+ houses]
The boy’s food [one boy]
The boys’ food [2+ boys]

You’ll see from the examples about houses and boys that the apostrophe really is important to show singular and plural. For the singular the apostrophe comes before the s, for the plural after the s.

If the plural is irregular — not formed by adding an s, the apostrophe comes before the s:

the mice’s tails [singular ‘mouse’, plural ‘mice’]

or follows the normal rule:

the sheep’s wool (one sheep)
the sheeps’ wool (more than one sheep)

Fortunately there are very few nouns in English that have an irregular plural!

Special plurals

This is perhaps the area that causes most confusion as the rules are less fixed. Current fashion seems to be increasingly to avoid the apostrophe in examples 2 and 3. Whichever version you prefer, at least be consistent though.

1. Letters

Dot the i’s and cross the t’s

The apostrophe is needed here simply to avoid ambiguity. Dot the is wouldn’t make sense.

2. Numbers

The 1980’s
The 1980s (also correct)

3. Abbreviations

There are over 600 MP’s
There are over 600 MPs (also correct)

Always wrong

Tomatoe’s £1 per kg

No apostrophe: this is plural, not possession

His, hers and it’s

If you add an apostrophe to its you change the meaning. Its without an apostrophe is the possessive pronoun and never has an apostrophe, it’s with an apostrophe means it is.

This is mine, that is your’s

If you add an apostrophe to yours it means your is — that’s grammatically wrong and doesn’t mean anything at all!

Yours is a possessive pronoun and never has an apostrophe. Again, for grammar junkies, the possessive pronoun is the genitive case of the personal pronoun. Here’s the full set of possessive pronouns (with not an apostrophe in sight):

Yours (singular)
Yours (plural)

Who’s and whose

Who’s and whose get confused because they are pronounced identically, but again the difference are quite simple as they follow the same principles as above:

  • Who’s means who is (the apostrophe shows there is a missing letter)
  • Whose shows possession

Whose house is that? (Who owns that house)?
Who’s knocking at the door (Who is knocking at the door)?

Apostrophe animated gif