Apostrophes have 2 main purposes:

  • to indicate missing letters in contracted verbs and negatives
  • to show possession and other relationships between nouns.

Apostrophes in contractions

Apostrophes indicate missing letters in contracted words and phrases:

I’m [I am]     you’re [you are]     there’s [there is]

she’ll [she will]     we’ll [we will]     who’d [who would]

can’t [cannot]     don’t [do not]     wouldn’t [would not]   

These contractions are particularly common in informal kinds of writing and when representing speech:

I’m fine, thanks.

I can’t believe she doesn’t like chocolate.

Don’t sit on that chair!

Some contractions with apostrophes sound the same as regular pronouns, but are clearly different when written. Take care when using these, as they are often misused:

it’s [it is]     It’s a sunny day.
its [possessive form of it]     The house was derelict; its windows were broken.

you’re [you are]     You’re too kind!
your [possessive form of you]     Your work is impressive.

they’re [they are]     They’re going to be late.
their [possessive form of they]     Their car has broken down.
there [at that place]     They will leave the car there.

who’s [who is]     Who’s going to the party?
whose [possessive form of who]     Whose clothes are these?

Apostrophes can express different relationships between 2 successive nouns:

  • possession – when the first noun or name owns the second, or the second noun belongs to the first
  • attribution – when the first noun or name is the site or source of the second
  • expressions of time – when the first noun is a single unit of time that defines the scope of the second noun.

The way in which the apostrophe is used depends on whether the first noun is singular or plural.

Singular nouns

To show possession with singular nouns (common or proper) and proper names, add an apostrophe followed by s:

a dog’s bone [the bone belonging to the dog]     the truck’s headlights     Dr Smith’s car     Lady Mary’s smile    

Do the same to show attribution:

Australia’s population [the population of Australia]     Earth’s circumference     Japan’s politics
Sydney’s traffic     Plato’s philosophy     the Royal Commission’s recommendations

And follow the same rule for singular nouns that already end in s:

the boss’s job description     the glass’s shape     James’s car     Tacitus’s Histories     Jesus’s teachings

Plural nouns

To show possession or attribution for plural nouns ending in -s or -es, add an apostrophe only:

cactuses’ spines     employees’ wages     students’ grades     state governments’ response

For the plural possessives of names that already end in s, make the noun plural in the standard way, then follow with an apostrophe:

the Joneses’ house     the Thomases’ children

Expressions of time

Use apostrophes in expressions that are based on singular units of time:

an hour’s delay     in 1 day’s time     a month’s salary     next week’s plan 

but not in expressions of plural time periods.

When not to use apostrophes

Do not use apostrophes:

  • in expressions of plural time periods
in 3 weeks time     after 4 years delay     6 months salary    
  • in plural nouns, even when the base word looks unusual with plural s

avocados [not avocado’s]     skis [not ski’s]     tattoos [not tattoo’s]

She ate 3 avocados in a single sitting.

I own 4 pairs of skis.

His back was covered in tattoos.

  • in plurals of dates and other numbers
1990s     the early 2000s     people in their 20s and 30s
  • in plurals of acronyms and initialisms
CVs     KPIs     SUVs     URLs

  • in Australian placenames that include possessives

    Frenchs Forest     Kings Cross     Paddys River     St Helens

    See the Place Names(Opens in a new tab/window) tool for a list of place names in Australia.

  • in the names of diseases that include a person’s name (see Human diseases and conditions)

    Crohn disease     Down syndrome     Huntington disease

    In everyday English, the older possessive form of these disease names is commonly used. It often persists in the names of nonprofit and research organisations that relate to these diseases (e.g. Parkinson’s Australia, Australian Alzheimer’s Research Foundation). Check the names of such organisations and use their official names.

  • with plural nouns that are descriptive rather than possessive or attributive

    drivers licence [a licence for drivers]     farmers market     girls high school     officers mess    

    Australasian Medical Writers Association     Willoughby Girls High School 

    But note that some organisations or institutions have chosen to retain the apostrophe – check the names of organisations and use their preferred form

National Farmers’ Federation     Department of Veterans’ Affairs

Did you know? A quick trick can help you decide whether a plural noun needs an apostrophe (i.e. is possessive or attributive) or not (i.e. is descriptive).

In many cases, an apostrophe is not needed if for rather than of would fit the sentence.

So:

  • the traditional recipe of my mother-in-law (not for my mother-in-law) = my mother-in-law’s traditional recipe [possessive]
  • the eve of New Year (not for New Year) = New Year’s Eve [attributive]
  • a college for teachers (not of teachers) = teachers college [descriptive]
  • a licence for drivers (not of drivers) = drivers licence [descriptive]

In some cases, either for or of could apply. For example, the National Farmers’ Federation could be either a federation for farmers or a federation of farmers; hence the need to check the preferred form for organisation names.