Even Oxford professors get apostrophes wrong. But there are simple rules to remember in order to get it right.
Apostrophes have two uses. First, they indicate that some letters have been taken out of a word to shorten it. For example: Do not becomes don’t; has not becomes hasn’t and will not becomes won’t. The apostrophe shows where the letter or letters have been removed. Apostrophes are used this way when writing informally.
Second apostrophes indicate that something belongs to or is connected with something else. To show this you use an ‘s. For example, the monkey’s tail means that the tail belongs to the monkey. The magazine’s readers means that the readers are connected with the magazine.
Crucially, apostrophes do not indicate the plural case.
Usually an apostrophe goes before the ‘s’. But if the owner is plural then the apostrophe goes after the ‘s’ that is already there. For example, the cats’ pyjamas says that the pyjamas belong to some (ie more than one) cats. The girls’ shoes means that the shoes belong to some girls.
If the owner’s name ends with an ‘s’, ask yourself how you would say it. For example St James’s Park and Bridget Jones’s Diary are correct. The Times’s crossword is incorrect.
When plurals don’t end in ‘s’ (words such as ‘men’ and ‘children’ use ‘s to show possession. For example: The men’s trousers – says that the trousers belong to the men. The women’s hats indicates that the hats belong to the women.
Watch out for its and it’s. It’s means ‘it is’: eg It’s freezing today. Otherwise use its as a possessive as in the penguin fell on its bottom due to the fact that it’s freezing today.
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