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？
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。
