Apostrophes can often cause confusion, but the rules for their use are straightforward.
An apostrophe has two uses, to indicate a missing letter in compound words (or contractions), and to indicate possession.
Contractions which use apostrophes are nearly always abbreviations and are therefore considered informal, meaning their use in essays is not advised apart from in direct quotations. Common examples include:
- Abbreviations of the verbs to be and to have in certain tenses, e.g. I’m for I am, you’ll for you will, he’d for he had, they’ve for they have.
- Negative verb phrases using not, e.g. don’t for do not, aren’t for are not, can’t for can not.
Apostrophes are used to indicate possession through the ‘apostrophe-s’ construction (’s), which indicates possession in the same way as an ‘of’ clauses. For example:
- He was the son of his father
Can also be written as
- He was his father's son
If the possessive noun if plural and already ends in ‘s’ (e.g. ‘fathers’), the ‘s’ in the apostrophe-s construction is dropped. So, for example:
- It was my brothers’ turn to wash the dishes;
- She tried to take the babies’ sweets
Writing brothers’s or babies’s in the above examples is a common mistake. But for a singular noun which ends in ‘s’, the second ‘s’ is included:
- He snapped the double bass’s string
- Everybody admired the princess’s dress
Likewise, plurals which do not end in ‘s’ also take the ‘apostrophe-s’, for example:
- The cows ate the sheep’s grass
This is the only situation where an ‘apostrophe-s’ appears in a plural noun, possessive or otherwise - an ‘apostrophe-s’ is never used to make a noun plural.
The use of apostrophes with pronouns requires special attention.
Apostrophes are only ever used with pronouns to form a contraction. Pronouns have their own possessive forms - my, your, his, its, our/ours, their/theirs. These never take the ‘apostrophe-s’ construction - your’s, our’s, their’s etc do not exist. Its and it’s are commonly confused, but following the rule above, its is the possessive form and it’s is a contraction of it is.
The same is true of your/you’re, his/he’s, their/they’re and theirs/there’s - if it has an apostrophe, it is a contraction, if it does not, it is a possessive.