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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): We use 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.

For example: I must finish this report by Friday. (The speaker feels it's important.)

• Strong Obligation (External Rule/Necessity): We use have to when the obligation comes from an external rule, law, or situation.

For example: We have to wear a uniform at school. (It's a school rule.)

• Advice or Weaker Obligation: We use should or ought to for recommendations, advice, or when something is generally a good idea.

For example: 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.

For example: I was supposed to call him yesterday, but I forgot.

• No Obligation: We use don't have to, don't need to, or needn't when something is not necessary.

For example: You don't have to come if you're busy.

• Strong External Obligation (making someone do something): We can use verbs like make or force to describe when someone else causes an obligation.

For example: 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: We use can for general permission. May is more formal.

For example: Can I use your pen? (Asking for permission)

For example: You can leave early today. (Giving permission)

• Having Permission: We use be allowed to or can to state that permission exists.

For example: Students are allowed to use their phones during the break.

• No Permission / Prohibition: We use mustn't or can't to say something is not allowed or is prohibited. Mustn't is stronger and often implies a rule or danger.

For example: You mustn't smoke in here. (It's against the rules.)

For example: You can't park here. (It's not permitted.)

• Allowing someone to do something: We use the verb let to give permission for someone to do something.

For example: My parents let me stay out late.

Past Forms of Obligation and Permission

We can also talk about past obligations and permissions.

• Past Obligation: We use had to for past necessities or rules.

For example: 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.

For example: They were supposed to arrive an hour ago.

• Past Permission: We use could or was/were allowed to. Could is for general past permission, while was/were allowed to is for specific instances.

For example: When I was a child, I could play outside until dark. (General)

For example: Yesterday, I was allowed to leave work early. (Specific)

• Past No Permission / Prohibition: We use couldn't or wasn't/weren't allowed to.

For example: We couldn't use our phones during the exam.

Summary of Obligation and Permission Expressions (B2)

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

Examples

• 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.

Practice

Common mistakes for Spanish speakers

Confusing mustn't and 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

While 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).

Frequently asked questions

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'?

We use 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?

No, must does not have a past form for obligation. Instead, we use had to. For example, I had to leave early yesterday.

Related lessons

• Modal verbs
• Modal verbs
• Modal verbs
• Modal verbs