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used to say that something is necessary or very important (sometimes involving a rule or a law) （表示必要或很重要）必须 All visitors must report to reception. 所有来宾必须到接待处报到。 Cars must not park in front of the entrance (= it is not allowed). 车辆不得停在入口处。 - (formal)
I must ask you not to do that again. 我得劝你别再那样做了。 You mustn't say things like that. 你千万别说那样的话。 I must go and get the kids from school. 我必须去学校接孩子们。 I must admit (= I feel that I should admit) I was surprised it cost so little. 我得承认，这么便宜，真让我惊讶。 - (especially British English)
Must you always question everything I say? (= it is annoying) 我说什么你都非要提出质疑吗？ ‘Do we have to finish this today?’ ‘Yes, you must.’ “我们今天一定得完成这工作吗？” “对，必须完成。”
Express Yourself Asking about obligationTopics Permission and obligationa1Asking about obligation 咨询相关义务 When you are unsure about what is expected of you in a situation, you can ask about obligations: 不确定在某种情境下该做什么时可以询问应履行的义务： What time do we have to be home? 我们必须在什么时候回到家？
Are we supposed to show our ID cards? 我们需要出示身份证吗？
Is it necessary to apply for a visa? 有必要申请签证吗？
Is there a legal obligation to wear a bike helmet here? 在这里骑自行车有没有法律规定要戴头盔？
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used to say that something is likely or logical （表示很可能或符合逻辑）一定 You must be hungry after all that walking. 走了这么远的路，你一定饿了吧。 He must have known (= surely he knew) what she wanted. 他一定早已知道她想要什么了。 I'm sorry, she's not here. She must have left already (= that must be the explanation). 抱歉，她不在这儿。准是走了。
Grammar Point must / have (got) to / must not / don’t have tomust / have (got) to / must not / don’t have toNecessity and Obligation 必要和义务 - Must and have (got) to are used in the present to say that something is necessary or should be done. Have to is more common in North American English, especially in speech:
You must be home by 11 o’clock. 你必须在 11 点之前回家。 I must wash the car tomorrow. 我明天必须洗汽车。 I have to collect the children from school at 3 o’clock. 我得在 3 点钟到学校接孩子。 Nurses have to wear a uniform. 护士必须穿制服。
- In British English there is a difference between them. Must is used to talk about what the speaker or listener wants, and have (got) to about rules, laws and other people’s wishes:
I must finish this essay today. I’m going out tomorrow. 我今天一定要完成这篇论文，因为我明天要出去。 I have to finish this essay today. We have to hand them in tomorrow. 我今天得完成这篇论文，因为我们明天必须交。
- There are no past or future forms of must. To talk about the past you use had to and has had to:
must 无过去和将来形式。表示过去用 had to 或 has had to： I had to wait half an hour for a bus 我得等半小时的公共汽车。
说将来的事用 will have to，如果已作好安排亦可用 have to： We’ll have to borrow the money we need. 我们需要的这笔钱只好去借了。 I have to go to the dentist tomorrow. 我明天得去看牙医。
- Questions with have to are formed using do:
带有 have to 的疑问句由 do 构成： Do the children have to wear a uniform? 孩子们必须穿制服吗？
在否定句中，用 must not 和 don't have to，但二者含义不同。must not 用于告诉某人不要做某事： Passengers must not undo their seat belts until the signs have been switched off. 在标志关闭之前，乘客不得解开安全带。
You mustn’t leave the gate open. 你一定不要让大门敞开着。
表示没有必要做某事用 don't have to： You don’t have to pay for the tickets in advance. 你不必预付票款。 She doesn’t have to work at weekends. 她周末不用上班。
Certainty 肯定 - Both must and have to are used to say that you are certain about something. Have to is the usual verb used in North American English and this is becoming more frequent in British English in this meaning:
He has (got) to be the worst actor on TV! 他无疑是最糟糕的电视演员！ - (British English)
This must be the most boring party I’ve ever been to. 这无疑是我参加过的最无聊的聚会。
说过去的事用 must have： Your trip must have been fun! 你这次旅行一定很开心吧！
- (especially British English)
used to recommend that somebody does something because you think it is a good idea （提出建议）应该，得 Grammar Point modal verbsmodal verbsTopics Suggestions and adviceb1- The modal verbs are can, could, may, might, must, ought to, shall, should, will and would. Dare, need, have to and used to also share some of the features of modal verbs.
can、could、may、might、must、ought to、shall、should、will 和 would 均为情态动词。dare、need、have to 和 used to 亦具有情态动词的某些特性。 - Modal verbs have only one form. They have no -ing or -ed forms and do not add -s to the 3rd person singular form:
情态动词只有一种形式，没有 -ing 或 -ed 形式，第三人称单数也不加 -s： He can speak three languages. 他会说三种语言。 She will try and visit tomorrow. 她明天将设法去参观。
- Modal verbs are followed by the infinitive of another verb without to. The exceptions are ought to, have to and used to:
情态动词后跟不带 to 的动词不定式，但 ought to、have to 和 used to 例外： You must find a job. 你必须找到一份工作。 You ought to stop smoking. 你应当戒烟。 I used to smoke but I gave up two years ago. 我过去抽烟，但两年前就戒了。
- Questions are formed without do/does in the present, or did in the past:
疑问句现在时不用 do/does，过去时不用 did： Can I invite Mary? 我可以邀请玛丽吗？ Should I have invited Mary? 我本该邀请玛丽吗？
- Negative sentences are formed with not or the short form -n’t and do not use do/does or did.
否定句用 not 或简约式 -n't，不用 do/does 或 did。
情态动词的不同用法可参考本词典里各情态动词词条。 - The modal verbs are can, could, may, might, must, ought to, shall, should, will and would. Dare, need, have to and used to also share some of the features of modal verbs.
Word OriginOld English mōste, past tense of mōt ‘may’, of Germanic origin; related to Dutch moeten and German müssen.
Idioms
if you must (do something)
must-see/must-read/must-have, etc.
used to tell people that something is so good or interesting that they should see, read, get it, etc. 必看（或必读、必备等）
needs must (when the Devil drives)
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in certain situations it is necessary for you to do something that you do not like or enjoy （情势所迫）只好如此；不得已而为之