Apostrophes are used to indicate possession or contraction.

Possession

After singular nouns, plural nouns which do not end in s and indefinite pronouns, use ’s.

For example:

  • I have found Rachel’s laptop.
  • All female staff are entitled one year’s statutory maternity leave.
  • It is everyone’s responsibility.

Note: The possesive form of the pronoun 'it' does not use an apostrophe. For example: 'The cat's fur was black. Its eyes were yellow.'

With personal names that end in an s, use ’s if you would normally pronounce an extra s in speech.

For example:

  • Dr Edwards’s research
  • Thomas’s camera
  • St James’s Park

Note, there are some exceptions to this rule, especially in the names of places or organisations, for example St Thomas’ Hospital.

After plural nouns ending in s, use s’

For example:

  • Academics’ workload (the workload of several academics)
  • Volunteers’ t-shirts

For compound nouns, and when multiple nouns are linked to make one concept, the apostrophe should be placed at the end of the final part.

For example:

  • the Mayor of London’s proposal

Contraction

Apostrophes are used to indicate where letters have been omitted. The apostrophe comes in the position where the letters have been omitted, not where the space was between the original words.

For example:

  • Don’t be afraid of Open Source
  • I’ll think about it.

Common mistakes with apostrophes

Apostrophes are often misused. Below are some common mistakes to avoid:

Plural nouns

Apostrophes should never be used for a plural noun (unless it is to indicate possession: see above).

For example:

  • The spring flower’s were in bloom
  • Student’s should arrive 20 minutes before the examination begins.

'It's' and 'its'

It’s should only be used to signify ‘it is’ or 'it has', and should not be used to indicate possesion. The possesive form of 'it' is 'its'.

For example:

  • Correct: It’s a beautiful day
  • Incorrect: The fossilised creature carried it’s young in pouches tethered to it’s body

'Who's' and 'whose'

Who’s (meaning ‘who is’) should not be used to mean ‘whose’ (indicating possession).

For example:

  • Correct (informal): Who’s attending the dinner?
  • Incorrect: The student, who’s dissertation won an award, graduated in May 2015.