基礎 · Unit 34
助動詞 (must / have to)
must 和 have to 都表示「必須 」的義務，但是must 表示說話者強烈的判斷·確信，have to 表示規則·情況所造成的外在必要，而且否定形 must not(禁止)和 don't have to(不必要)的意思幾乎完全相反。
概念說明
must 和 have to 都表示「必須 ~」的義務，但是must 表示說話者強烈的判斷·確信，have to 表示規則·情況所造成的外在必要，而且否定形 must not(禁止)和 don't have to(不必要)的意思幾乎完全相反。
A. must — 強烈的義務·確信
must 是助動詞，不管主詞是什麼形態都不變，用來表示說話者強烈感受到的義務，或是邏輯上幾乎確定的推測。形態永遠是 must + 原形動詞。
| 用途 | 意思 | 例子 |
|---|---|---|
| 強烈的義務 | 一定要 ~ | You must study hard. |
| 規則·法律 | 非 ~ 不可 | Drivers must stop at red lights. |
| 強烈的確信 | 一定是 ~ | He must be at home. |
| 命令·警告 | 務必要 ~ | You must try this cake. |
- You must finish your homework before dinner. (晚餐前一定要把功課做完。)
- Students must wear their ID cards. (學生一定要配戴學生證。)
- Anna must be very smart. (Anna 一定非常聰明。)
- You must see this movie. (這部電影你一定要看。)
B. have to — 外在的義務·必要
have to 表示規則·法律·周遭情況所造成的外在必要，第三人稱單數會變成 has to，而且可以自由變化成過去·未來等各種時態。如果說 must 是個人的判斷，那 have to 就帶有「已經定好了，沒辦法」的語感。
| 時態 | 形態 | 例子 |
|---|---|---|
| 現在 (I / you / we / they) | have to | I have to work today. |
| 現在 (he / she / it) | has to | She has to leave now. |
| 過去 | had to | We had to wait in line. |
| 未來 | will have to | You will have to try again. |
- I have to submit the report by Friday. (我必須在星期五之前交報告。)
- He has to take medicine every morning. (他每天早上都得吃藥。)
- We had to cancel the trip last week. (我們上禮拜不得不取消旅行。)
- You will have to speak louder in the meeting. (開會的時候你得講大聲一點。)
C. must not (禁止) vs don't have to (不必要) — 否定形對比
must not 是「絕對不可以做」的強烈禁止，don't have to 是「沒有必要做」的不必要，兩者的意思幾乎完全相反。請把 must not = 禁止 / don't have to = 不必要 這組對比整個記起來。
| 形態 | 意思 | 例子 |
|---|---|---|
| must not (mustn't) | 不可以做 (禁止) | You mustn't tell anyone. |
| don't have to | 沒必要做 (不必要) | You don't have to tell anyone. |
| doesn't have to | (第三人稱) 沒必要做 | She doesn't have to come. |
| didn't have to | (過去) 當時沒必要做 | We didn't have to pay. |
- You mustn't enter this room. It's private. (不可以進這個房間。這是私人空間。)
- You don't have to enter this room. It's optional. (不一定要進這個房間。這是自由選擇的。)
- Children mustn't play with fire. (小孩絕對不可以玩火。)
- She doesn't have to work on Sundays. (她星期天不必上班。)
重點整理
- 1must 是助動詞，第三人稱單數也不會變成 musts，後面一定接原形動詞。(例: She must go. — She musts go. 是錯的)
- 2have to 的時態變化很自由，第三人稱單數 has to、過去 had to、未來 will have to。(例: She has to / We had to / You will have to)
- 3must not(禁止)和 don't have to(不必要)的意思完全相反，絕對不能混著用。(例: You mustn't tell = 禁止 / You don't have to tell = 不說也可以)
- 4must 表示說話者個人的判斷·強烈確信，have to 表示規則·情況造成的外在必要。(例: I must = 我自己的決心 / I have to = 沒辦法只好如此)
- 5must 本身沒有過去·未來時態，所以要借用 have to 說成 had to / will have to。(例: I had to leave early yesterday.)
例句
You must wear a seatbelt in the car.
在車上一定要繫安全帶。
Students must arrive by 9 AM.
學生必須在早上九點前到。
You must try this restaurant sometime.
你哪天一定要去試試這家餐廳。
Anna must be very tired after that trip.
Anna 那趟旅行之後一定很累。
I have to leave early tomorrow morning.
我明天早上得早點出門。
這個單元還有更多例句。註冊後可以看完整內容並聆聽發音。
容易犯的錯誤
She must study harder.
You don't have to come if you're busy.
I must finish this today.
He has to leave now.
We had to wait for an hour.