We use the apostrophe for three reasons.
To show that a letter or letters are missing
- I'm going to the zoo.
- You can't feed the animals.
- It's a lovely day out, isn't it?
To show possession
In the singular, the apostrophe comes before the 's'. In the plural it comes after the 's'.
- The girl's idea was accepted. (Singular - the idea a girl has had)
- The girls' idea was accepted. (Plural - an idea a group of girls has had)
- The company's management must tackle this. (The management of one company)
- The companies' management must tackle this. (The management of several companies)
If a plural noun doesn't end in 's', we add an apostrophe and an 's'.
- This is the people's choice.
- We invited the children's parents to this event.
With names or singular nouns that end in 's', 'x' or 'z', we usually add an apostrophe followed by 's'.
- The bus's journey came to an end.
- The fox's den was well hidden.
- Liz's bag cut into her shoulder.
However, if it sounds better, it is acceptable to just add the apostrophe.
- Karl Benz' vehicle was the first to be driven by an internal-combustion engine.
- Euripides' plays show innovation.
In some expressions of time
- We have been given a week's notice. (Singular)
- We have been given two weeks' notice. (Plural)
When apostrophes must not be used
Normal plurals don't need an apostrophe.
- We sell oranges and lemons.
- The 1980s are a blur.
- MPs debating this today.
- People in their 70s need to renew their licence every three years.
The word 'its', used to show possession, doesn't have an apostrophe. 'It's' with an apostrophe means 'it is' or 'it has'.
- The company now has its own car park. It's to the rear of the building. It's been there for about a year now.
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