144 must 和 have to 的各种形式
A must
must 是情态动词。（参见第107节B。）它用于现在时和将来时。
否定式：must not／mustn't
疑问式：must I？等
否定疑问式：must I not？／mustn't I？等
过去时用 had to 代替。
must 与不带 to 的不定式（即动词原形）连用。
它可表示义务和语气较强的劝告：
Father：You must get up earlier in the morning．父亲：你早晨必须起早一点。（义务）
You must ta
ke more exercise．Join a squash club．
你应该多锻炼。参加一个壁球俱乐部吧。（劝告）
B have to
| |
义务 |
外部的权力 |
无义务 |
| 将来时 |
must |
shall/will have to |
shan't/won't have to |
| 现在时 |
must |
have to |
don't/doesn't have to |
| |
|
have (got) to |
haven't (got) to |
| 过去时 |
had to |
had to |
didn't have to |
| |
|
|
hadn't (got) to |
*请见下面C。
C 带星号的 have to 各形式间的区别
have to（不带 got）与否定式 don't／doesn't have to 是表示习惯性行动的正确形式，但也可以用于表示一次性行动。在美国英语中是普遍使用的。
have（got）to 和 haven't（got）to 只用于表示一次性行动：
Tom：I have to go to work every day except Sunday．But I don't have to
work a full day on Saturday．
汤姆：除了星期天外我必须每天去上班，但星期六我不必干一整天。但在星期天他可以说：
I'm glad I haven't（got to go to work today．／I'm glad I don't have to go to work today．
我真高兴，今天不必上班。
过去式 didn't have to 既可表示过去的习惯，也可表示一次性行动。
hadn't（got）to 多用于表示一次性行动。
didn't have to 是较为普遍的形式。
have to 在肯定句中表示“义务”。
have to 在否定句中表示“无义务”。这种意思也可由 need not，don't need 等来表示。（参见第 149节。） |
