In UK and US English, the apostrophe is used:
Personal pronouns (words like I, you, he, she, it, we, they) indicate the possessive by becoming a whole new word. These new words are already possessive, so they don't need an apostrophe: my, mine, your, yours, his, her, hers, its, our, ours, their, theirs. Note that none of them has an apostrophe.
It's means it is or it has. There's no such word as its'.
But we don't always use apostrophes:
In the cases where you wouldn't use an apostrophe in the singular, don't use it for the plural:
But we say this CD's broken because it's a short form of this CD is broken.
A few words are sufficiently confusing that we want to indicate to the reader how the word is constructed. The apostrophe can be used for this if it is really necessary, but mostly it isn't.
But you might consider:
There's no need for it in:
The apostrophe goes directly after the thing doing the possessing:
Note that we can often use for instead of of – shirts for the men. The possessive is much a looser concept than ownership: the girls may not own the school, but it's still a girls' school.
The apostrophe is used to show a connection between two things: if a dog has a bone, it's the dog's bone. But sometimes there is no possessive connection.
Sometimes the relationship is adjectival, not possessive:
The accounts don't have the department, and the sports don't have a car – it's a department of type "accounts", and a car of type "sports". We could just as well have written:
A department of type "marketing" and a car of type "two-door". Clearly not possessive.
Sometimes there's no thing to possess or be possessed:
There's no such thing as a "pregnant", and the twelve weeks can't have one, so the phrase is not possessive. We could say twelve weeks' notice and two years' experience, because there are such things as notice and experience, and in some sense they are linked to ("given by" if you like) the twelve weeks and the two years. (Technically, pregnant is an adjective, notice and experience are nouns. Possessive phrases need two nouns – one to possess and one to be possessed.)
The pregnancy is not linked to a "forty-week". In forty weeks' pregnancy, the pregnancy is linked to forty weeks.
You sometimes see She walk's the dog, but this is wrong. The walks here is not the possessive of a walk, but the present tense of the verb to walk. Verbs never take possessive apostrophes. It should be she walks the dog.
This is also wrong – there's nothing in the sentence to be possessed by the CD or the video. It should be plural, not possessive: CDs and videos for sale. It would be OK to say the CD's label was coming off, and the video's price was wrong, because the CD does have a label, and the video does have a price.
Sometimes it's just a plural:
Some usage is not settled. Debate rages over James's book and James' book, over Farmers Market and Farmers' Market. If accounts department doesn't need an apostrophe, what about customers car park?
Ask questions and debate any language point at our discussion board. Everyone is welcome.
Please feel free to link to this page.
Last update: June 2012.