have to与must这两个动词均有“必须、不得不”之意。
have to : 通俗用语，指受客观条件或环境迫使而“不得不”做某事，突出客观性。
- I have to go to San Francisco tomorrow on business.
我明天得去旧金山出差。 - What time do you have to be there?
你得几点钟到那儿？ - Do we have to finish this today?
我们今天必须把这事做完吗？ - We'll have to start keeping detailed records.
我们不得不开始作详尽的记录。 - Jackie's ill so they've had to change their plans.
杰基病了，因此他们不得不改变计划。
must : 通常表示命令或说话人主观认为必须要做某事，含强调语气，侧重主观性。
- Meat must be cooked thoroughly.
肉必须完全煮熟。 - I must get some sleep.
我必须睡会儿觉了。 - You mustn't show this letter to anyone else.
你不许把这封信给其他人看。 - Luggage must not be left unattended (= it is against the rules).
行李不能无人看管。 - Must you leave so soon?
你非得走这么早吗？ - "Must I sign this?" "Yes, you must."
“我必须在这上面签字吗？”“是的，必须。”
