說明

must 偏主觀（自己覺得必須），have to 偏客觀（外部條件要求），否定形式意思差別很大：mustn't 是禁止，don't have to 是不必。

同類條目

• 主謂一致：就近原則 —— Either you or he is right.
• 現在完成時 vs 一般過去時 —— I have lived here for 5 years. / I lived there in 2010.
• 定語從句：that 與 which —— The book that/which I bought is good.
• 虛擬語氣：if 條件句 —— If I were you, I would take it.
• 非謂語：doing 與 to do —— I enjoy reading. / I want to go.
• 倒裝：否定詞提前 —— Never have I seen such a thing.
• 比較級：as ... as 與 than —— He is as tall as I am. / He is taller than I am.
• 情態動詞表推測 —— It must be true. / It can't be true.