「必须」和「应该」

两档语气。一档硬，一档软。

你必须去。         You must go. / You have to go.
你应该去。         You should go.

必须 = 没得选 应该 = 建议、道理上该

三档力度

中文	英文	力度
必须 / 一定要	must / have to	最硬
应该	should / ought to	中等
最好	had better	温柔但严重

must vs have to

must       →  内在压力（自己觉得必须）
have to    →  外在压力（被要求）

I must finish this.        我得写完（自己要完成）。
I have to work late.       我得加班（老板让）。

日常口语 have to 更常见。must 偏书面或强烈。

动手

我必须走了。

✅ I have to go. / I gotta go.

你应该多休息。

✅ You should get more rest.

最好别说出去。

✅ You'd better not tell anyone.

这不必。

✅ You don't have to.

否定是个大坑

must not     →  禁止（不能！）
don't have to →  没必要（不必做）

You must not go.        你不能去（不准）
You don't have to go.   你不必去（可去可不去）

must not ≠ don't have to —— 中文的"不必"对应的是后者。

小卡片

必须 / 一定要   →  must / have to / gotta
应该           →  should / ought to
最好           →  had better
不必           →  don't have to
不能 / 不准     →  must not / can't

——下一课：「打」。