What are Modals of Obligation?
Modals of obligation are verbs that show how necessary or important an action is. They come before the main verb in a sentence.
These verbs help us express rules, duties, advice, and things that are not allowed or not necessary.
- Must et have to show strong obligation or necessity.
- Mustn’t et can’t show prohibition (something is not allowed).
- Don’t have to shows a lack of obligation (something is not necessary).
- Should et ought to give advice or recommendations.
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When to Use Must et Have To?
Must et have to both express obligation, but there is a small difference in how we use them.
- Nous utilisons must when the speaker feels the obligation strongly. It often comes from an internal feeling or a rule the speaker makes for themselves.
- Nous utilisons have to when the obligation comes from outside, like a rule, law, or another person's authority.
In spoken English, have to is more common than must for general obligations.
Talking About Things That Are Not Allowed: Mustn't et Can't
When something is forbidden or not permitted, we use mustn't ou can't.
- Mustn't (ou must not) is used for strong prohibitions, often from the speaker or a very important rule.
- Can't (ou cannot) also shows prohibition, often referring to rules made by others or general impossibility.
When Something Is Not Necessary: Don't Have To
If there is no obligation to do something, or it is not necessary, we use don't have to.
- This means you can do it if you want, but it's not required.
- It is very different from mustn't, which means you are not allowed to do something.
Giving Advice and Recommendations: Should et Ought To
To give advice or suggest something is a good idea, we use should ou ought to.
- These modals show a weaker obligation than must ou have to.
- Should is much more common than ought to, especially in everyday conversation.
- The negative forms are shouldn't et ought not to.
Past and Future Obligations
The modal must does not have a past or future form. For past and future obligations, we always use have to.
- For the past, use had to.
- For the future, use will have to.
| Modal Verb | Signification | Exemple |
|---|---|---|
| Must | Strong obligation, often personal or internal. | I must remember her birthday. |
| Have to | Strong obligation, external rule or necessity. | Students have to wear a uniform. |
| Mustn't | Prohibition (not allowed). | You mustn't touch that. |
| Can't | Prohibition (not allowed), often external rule. | We can't use phones in class. |
| Don't have to | Lack of obligation (not necessary). | You don't have to come if you're busy. |
| Should | Advice, recommendation, what is right. | You should get more sleep. |
| Ought to | Advice, recommendation (similar to should). | We ought to recycle more. |
| Had to | Past obligation. | I had to leave early. |
| Will have to | Future obligation. | We will have to reschedule. |
Exemples
- I must study for my exam tonight. (Personal necessity)
- You have to wear a seatbelt in the car. (External rule/law)
- We mustn't make noise after 10 PM. (Strong prohibition)
- You can't park here; it's a no-parking zone. (External rule/prohibition)
- She doesn't have to work on Sundays. (Not necessary)
- You should visit the museum; it's fantastic. (Advice)
- They ought to apologize for their behavior. (Recommendation)
- Yesterday, I had to finish my report. (Past obligation)
- Tomorrow, we will have to wake up early. (Future obligation)
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Spanish speakers often make mistakes with modals of obligation, especially confusing prohibition and lack of necessity.
- Mustn't vs. Don't have to: A common error is using don't have to when you mean mustn't. In Spanish, "no tener que" means "not have to" (no obligation), but sometimes learners use it incorrectly to mean "it's forbidden."
Incorrect: You don't have to smoke here. (This means 'it's not necessary to smoke here', which is strange.)
Correct: You mustn't smoke here. (This means 'it's forbidden to smoke here.') - Must vs. Have to for external rules: While must can sometimes be used for external rules, have to is generally more natural for obligations imposed by others or by law.
Less natural: You must buy a ticket before boarding.
More natural: You have to buy a ticket before boarding. - Using must in the past/future: Remember that must does not have past or future forms. Always use had to ou will have to.
Incorrect: I musted go yesterday.
Correct: I had to go yesterday.
Questions fréquemment posées
What is the main difference between must and have to?
The main difference is the source of the obligation. Must often expresses a personal or internal feeling of necessity (e.g., I must call my mom). Have to usually expresses an external obligation, like a rule or law (e.g., You have to pay taxes).
Can I use 'have got to' instead of 'have to'?
Oui, have got to is very common in informal spoken English and means the same as have to. For example, I've got to go now means I have to go now.
Is there a difference between 'should' and 'ought to'?
They have the same meaning and are used to give advice or recommendations. Should is much more common in everyday English. Ought to can sound a little more formal or slightly stronger, but the difference is minimal.
How do I talk about past obligations?
For past obligations, you must use had to. For example, I had to work late last night. You cannot use must in the past tense.
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