否定式的常见缩写形式
系动词be、助动词、情态动词的否定形式一般可以缩写成为一种简略的形式。如：
is not—isn’t are not—aren’t
was not—wasn’t were not—weren’t
has not—hasn’t have not—haven’t
will not—won’t would not—wouldn’t
shall not—shan’t should not—shouldn’t
do not—don’t did not—didn’t
ought not—oughtn’t dare not—daren’t
used not to—usedn’t / didn’t use to
