1. 表示“必須”、“一定要”
(1) 可用于肯定句、否定句或疑問句；用于否定句時(shí)，mustn't 的意思是“一定不要”、“不能”，而不是“不必”：You must finish it today. 你一定要在今天完成它。You must see the doctor. 你一定要看醫(yī)生。Must you go so soon? 你一定得這么早就走嗎?We mustn't think only of ourselves. 我們可不能只考慮自己。

(2) 主要表示現(xiàn)在或?qū)?，但有時(shí)(如在間接引語中)也可表過去(=had to)：She asked if she must (had to) leave. 她問她是否一定要離開。

(3) 對(duì)于must 開頭一般疑問句，若要作否定回答，可用needn't，不用mustn't："Must I come over tonight?" "No, you needn't." “我今晚必須過來嗎?”“不必。”

(4) 其后可接被動(dòng)結(jié)構(gòu)或進(jìn)行形式：Something must be done to stop it. 必須采取措施來阻止它。I think I must be going. I think I must be going. 我想我得走了。2. 表示推測(cè)。意為“準(zhǔn)是”、“一定是”(1) 通常只用于肯定句，在否定句或疑問句用 can 代之：It must be true. 那一定是真的。It must be true. 比較：Can it be true?? 那可能是真的嗎? / It can't be true. 那不可能是真的。(2) 后接動(dòng)詞原形，表示對(duì)現(xiàn)在情況的推測(cè)： He must be wrong. 他一定錯(cuò)了。The man must have a lot of money. 這個(gè)人一定有不少錢。注：must 表示對(duì)現(xiàn)在情況的推測(cè)后接動(dòng)詞原形時(shí)，該動(dòng)詞通常為狀態(tài)動(dòng)詞(如 be, have, know 等)，若為動(dòng)作動(dòng)詞，通常要轉(zhuǎn)換其它說法?！八欢〞?huì)贏”，通常不說He must win，可說He is sure to win。(He must win的意思是“他必須要贏”)?(3) 其后可接進(jìn)行式或完成進(jìn)行式，用以談?wù)撘粋€(gè)正在進(jìn)行的動(dòng)作：He must be writing a letter to his girl friend. 他一定在給他女朋友寫信。Someone must have been smoking here．一定有人一直在這里抽煙。(4) 后接不定式的完成式，用來談?wù)撘寻l(fā)生的情況：He must have arrived already．他一定已經(jīng)到了。I didn't hear the phone. I must have been asleep. 我沒有聽到電話鈴，我一定是睡著了。3. 表示“應(yīng)當(dāng)”。相當(dāng)于should, ought to的意思You must say hello to her．你應(yīng)當(dāng)跟她打個(gè)招呼。We must go and have a weekend there．我們應(yīng)當(dāng)?shù)侥抢锒戎苣?. 表示“偏偏”有時(shí)表示不巧，有時(shí)表示固執(zhí)，通常都是指令人不快的事：Must you make so much noise? 你就非得弄出這么大的聲音嗎？Why must you always interrupt me? 你為什么硬是老要打斷我？We were ready to leave, but the baby must catch cold.? 我們剛準(zhǔn)備好要走, 可孩子偏偏得了感冒。Just when I was busy, the neighbor must come and chatter. 正當(dāng)我忙碌的時(shí)候，鄰居偏偏過來聊天。正當(dāng)我忙碌的時(shí)候，鄰居偏偏過來聊天。