Did为一般过去时标志，它是do的过去时形式，如：
Did you go to see your Uncle in hospital?have当助动词则为完成时态的标志，它会根据主语的人称和单复数发生变化
如：Have you fished your homework?Has she gone to see her father in hospital?
此外，have 还有一个特殊的用法，仅限于美式英语：英式：Do you have a book?美式：Have you a book?若二者同时存在于一个句子中，一般是did在句首 you have the book?你以前有这本书吗?
