◊ GRAMMAR
A contraction is a shortened form in which a subject and an auxiliary verb, or an auxiliary verb and 'not', are combined to form one word.
I'm getting desperate.
She wouldn't believe me.
You use contractions when you are writing down what someone says, or when you are writing in a conversational style, for example in letters to friends.
The contracted forms of 'be' are used when 'be' is a main verb as well as when it is an auxiliary. The contracted forms of 'have' are not usually used when 'have' is a main verb.
The following table shows contractions of personal pronouns and 'be', 'have', 'will', 'shall', and 'would'.
◊ WARNING
You cannot use any of the above contractions at the end of a clause. You must use the full form instead. For example, you say 'I said I would', not 'I said I'd'.
◊ negative contractions
The following table shows contractions of 'be', 'do', 'have', modals, and semi-modals with 'not'.
◊ WARNING
There is no contracted form of 'am not' in standard English. In conversation and informal writing, 'I'm not' is used. However, 'aren't I?' is used in questions and question tags.
Aren't I brave?
I'm right, aren't I?
In standard English, a pronoun followed by a negative contraction of a modal or 'have' is more commonly used than a contraction followed by 'not'. For example, 'I won't', 'I wouldn't', and 'I haven't' are more common than 'I'll not', 'I'd not', and 'I've not'.
However, in the case of 'be', both types of contraction are equally common. For example, 'you're not' and 'he's not' are used as commonly as 'you aren't' and 'he isn't'.
You aren't responsible.
You're not responsible.
◊ modals and 'have'
The auxiliary 'have' is not usually pronounced in full after 'could', 'might', 'must', 'should', and 'would'. The contractions 'could've', 'might've', 'must've', 'should've', and 'would've' are occasionally used in writing when reporting a conversation.
I must've fallen asleep.
You should've come to see us.