What Do Obligation and Permission Mean?
In English grammar, ‘obligation’ refers to something you must do, or something that is necessary. It’s a duty or a requirement.
‘Permission’ means you are allowed to do something. It’s the opposite of prohibition.
How Do We Express Obligation?
We use different words to show how strong an obligation is, or where the rule comes from.
- Strong Obligation (Internal/Speaker's Rule): 我们使用 must when the speaker feels the obligation strongly or is giving a direct order. It often comes from an internal feeling or the speaker's authority.
例如： I must finish this report by Friday. (The speaker feels it's important.)
- Strong Obligation (External Rule/Necessity): 我们使用 have to when the obligation comes from an external rule, law, or situation.
例如： We have to wear a uniform at school. (It's a school rule.)
- Advice or Weaker Obligation: 我们使用 should 或 ought to for recommendations, advice, or when something is generally a good idea.
例如： You should study more for the exam. (It's advice.)
- Expected Obligation (often unfulfilled): Be supposed to indicates an expectation or a plan that might not happen.
例如： I was supposed to call him yesterday, but I forgot.
- No Obligation: 我们使用 don't have to, don't need to, 或 needn't when something is not necessary.
例如： You don't have to come if you're busy.
- Strong External Obligation (making someone do something): We can use verbs like make 或 force to describe when someone else causes an obligation.
例如： My boss made me work late.
How Do We Express Permission?
When we talk about permission, we are saying that something is allowed.
- Giving or Asking for Permission: 我们使用 can for general permission. May is more formal.
例如： Can I use your pen? (Asking for permission)
例如： You can leave early today. (Giving permission)
- Having Permission: 我们使用 be allowed to 或 can to state that permission exists.
例如： Students are allowed to use their phones during the break.
- No Permission / Prohibition: 我们使用 mustn't 或 can't to say something is not allowed or is prohibited. Mustn't is stronger and often implies a rule or danger.
例如： You mustn't smoke in here. (It's against the rules.)
例如： You can't park here. (It's not permitted.)
- Allowing someone to do something: 我们使用动词 let to give permission for someone to do something.
例如： My parents let me stay out late.
Past Forms of Obligation and Permission
We can also talk about past obligations and permissions.
- Past Obligation: 我们使用 had to for past necessities or rules.
例如： Yesterday, I had to work until midnight.
- Past Expected Obligation: Was/were supposed to indicates an expectation in the past that might not have happened.
例如： They were supposed to arrive an hour ago.
- Past Permission: 我们使用 could 或 was/were allowed to. Could is for general past permission, while was/were allowed to is for specific instances.
例如： When I was a child, I could play outside until dark. (General)
例如： Yesterday, I was allowed to leave work early. (Specific)
- Past No Permission / Prohibition: 我们使用 couldn't 或 wasn't/weren't allowed to.
例如： We couldn't use our phones during the exam.
| Function | Present | Past | Negative / No Obligation |
|---|---|---|---|
| Strong Obligation (Internal) | must | N/A (use had to) | mustn't (prohibition) |
| Strong Obligation (External) | have to / need to | had to / needed to | don't have to / don't need to / needn't |
| Advice / Weaker Obligation | should / ought to | should have + PP | shouldn't |
| Expected Obligation | be supposed to | was/were supposed to | not supposed to |
| Permission | can / may / be allowed to / let | could / was/were allowed to / let | can't / may not / not allowed to |
示例
- You must submit your assignment by Friday.
- I have to attend a meeting tomorrow morning.
- You should apologize for your mistake.
- We are supposed to meet at 7 PM.
- You don't have to pay for the tickets; they're free.
- Can I borrow your laptop for a moment?
- Students are not allowed to eat in the library.
- My parents let me travel alone when I was 16.
- He was forced to resign from his position.
- When I was younger, I could stay up late on weekends.
练习
西班牙语母语者常犯的错误
令人困惑 mustn't 和 don't have to
Spanish speakers sometimes confuse these because in Spanish, 'no tener que' (don't have to) can sound similar to 'no deber' (mustn't). However, their meanings in English are very different:
- You mustn't do that. (It is prohibited. It's a strong negative obligation.)
- You don't have to do that. (It is not necessary. There is no obligation.)
For example, if you say You mustn't pay, it means paying is forbidden. If you say You don't have to pay, it means paying is optional.
Overusing must for external obligations
虽然 must is correct for strong obligation, have to is more common for rules and laws that come from outside the speaker. For example, I have to pay my taxes is more natural than I must pay my taxes (unless you are emphasizing your personal internal commitment to paying them).
常见问题
What is the main difference between 'must' and 'have to'?
The main difference is the source of the obligation. Must usually expresses an internal obligation or the speaker's strong feeling about what is necessary. Have to expresses an external obligation, meaning the rule or necessity comes from outside the speaker (e.g., a law, a regulation, or a situation).
Can I use 'may' instead of 'can' for permission?
Yes, you can. May is more formal than can when asking for or giving permission. For example, May I come in? is more polite than Can I come in?
When do we use 'be supposed to'?
我们使用 be supposed to to talk about things that are expected or planned, often implying that they didn't happen or won't happen. It can also refer to general expectations or duties. For example, You're supposed to be here by 9 AM (it's expected).
Is there a past form for 'must' for obligation?
不，, must does not have a past form for obligation. Instead, we use had to. 例如，, I had to leave early yesterday.
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