形式或助动词will即have to, has to, had to和will have to的否定式分别为don't have to, doesn't have to, didn't have to和won't have to，疑问句是在句首加助动词do的相应形式，句中还原成have to或把will放到句首。

　What does she have to do? 她必须做什么？

　You didn't have to wait for me yesterday. 昨天你没有必要等我。

　⑶ have to和must 的区别

　① 含义和用法上的区别，have to强调客观需要做某事，即表示由于客观外界的条件的需要不得不做某事，含有"形势逼迫"的意味，must强调说话者主观上认为必须做某事，含有"主观判断"的意味。

　My bike was broken on my way to school. I had to walk there.

　我的自行车在上学的路上坏了， 我不得不走路去上学。

　We must learn English well. 我们必须学好英语。

　Must I finish the homework now? 我必须现在完成作业吗？

　Yes, you must. /No, you needn't. 是的，你必须现在完成。（不，你不必。）

③ need与have to 用法辨析

need表示需要，主要用于否定句和疑问句。用于疑问句，肯定回