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What Are Modal Verbs?

Modal verbs are special verbs that add extra meaning to the main verb in a sentence. They express things like possibility, ability, permission, or obligation.

For example, in I can speak English, can is the modal verb, and it tells us about ability.

When Do We Use “Must”?

Nous utilisons must to express a strong obligation or something that is necessary. This obligation often comes from the speaker's own feeling or from a very strict rule.

• Strong personal obligation: You feel it is important to do something. For example, I must study for my exam.
• Rules and laws (often written): These are usually formal and non-negotiable. For example, All visitors must report to reception.
• Recommendations or advice (strong): When you strongly advise someone. For example, You must try this cake; it's delicious!

When Do We Use “Have To”?

Have to also expresses obligation or necessity, but it usually comes from an external source. This means the obligation is due to a rule, a situation, or another person.

• External obligation: A rule, law, or situation makes it necessary. For example, I have to wear a uniform at work. (It's a company rule).
• General necessity: Something that is generally required. For example, Doctors have to work long hours.
• Common in spoken English: Have to is more common than must for everyday obligations in conversation.

What About “Can” for Permission?

Nous utilisons can to talk about permission or what is allowed. It's a common way to ask for and give permission.

• Giving permission: To say that something is allowed. For example, You can use my phone.
• Asking for permission: To politely ask if something is allowed. For example, Can I sit here?
• Ability: Can also expresses ability, meaning you know how to do something. For example, I can swim.

How Do We Form Sentences with These Modals?

The structure for these modal verbs is simple: modal verb + base form of the main verb (without to).

• Positive:
  Subject + must + base verb (par exemple, She must leave now.)
  Subject + have to / has to + base verb (par exemple, They have to study. / He has to work.)
  Subject + can + base verb (par exemple, We can go.)
• Negative:
  Subject + mustn't + base verb (par exemple, You mustn't talk.)
  Subject + don't have to / doesn't have to + base verb (par exemple, I don't have to cook. / She doesn't have to pay.)
  Subject + can't + base verb (par exemple, They can't enter.)

The Important Difference: “Mustn't” vs. “Don't Have To”

This is a key point for B1 learners! The negative forms of must et have to have very different meanings.

• Mustn't (ou must not): Means something is forbidden or prohibited. It is very important NOT to do it. For example, You mustn't smoke in the hospital. (It's against the rules and dangerous).
• Don't have to (ou doesn't have to): Means something is not necessary. You have a choice; you can do it if you want, but it's not an obligation. For example, You don't have to come to the meeting if you're busy. (It's optional).

How Do We Ask Questions?

Questions with must are rare in modern English. We usually use have to or other phrases to ask about necessity.

• For have to: Utilisation Do ou Does.
  Do I have to bring my passport?
  Does she have to work on weekends?
• For can: Invert the subject and can.
  Can I open the window?
  Can they speak French?

Summary of Must, Have To, and Can

Modal Verb	Meaning	Negative Form	Exemple
Must	Strong obligation, strict rule, internal necessity	Mustn't (Prohibition)	You must wear a helmet.
Have to	External obligation, necessity (rules, situations)	Don't have to (Not necessary)	I have to work late tonight.
Can	Permission, ability	Can't (No permission, inability)	You can use my computer.

Exemples

• You must finish your homework before watching TV.
• We have to pay our rent by the fifth of the month.
• Students mustn't cheat on exams.
• I don't have to wake up early tomorrow; it's a holiday.
• You can take a break now if you want.
• She can't come to the party because she's ill.

Entraînement

Erreurs courantes chez les hispanophones

Spanish speakers often make these mistakes:

• Using must to: Remember, modal verbs are followed directly by the base form of the verb, without to.
  Incorrect: I must to go.
  Correct: I must go.
• Confusing mustn't et don't have to: In Spanish, 'no tener que' (not have to) and 'no deber' (must not) are distinct. Make sure you use the correct English equivalent.
  Incorrect (if you mean 'not necessary'): You mustn't work today.
  Correct: You don't have to work today. (If it's not necessary)
  Correct: You mustn't touch that! (If it's forbidden)
• Incorrect conjugation of have to: Remember that have to changes to has to for third-person singular subjects (he, she, it).
  Incorrect: He have to study.
  Correct: He has to study.

Questions fréquemment posées

What is the main difference between 'must' and 'have to'?

The main difference is the source of the obligation. Must often comes from an internal feeling or a very strict, formal rule. Have to usually comes from an external rule, law, or situation, and is more common in everyday spoken English.

Can I use 'must' for past obligations?

Non, must does not have a past form. For past obligations, we use had to. For example, Yesterday, I had to work late.

Is 'can't' the same as 'mustn't'?

They are similar in meaning but can have slightly different nuances. Mustn't implies a strong prohibition or a rule that you are not allowed to break. Can't often means 'not allowed' or 'not possible'. For example, You mustn't park here is a strong rule, while You can't park here might be a general observation that parking is not permitted or there's no space.

Why are 'must' questions rare?

In modern English, asking questions with must (par exemple, Must I go?) sounds very formal or old-fashioned. We typically use Do I have to...? ou Is it necessary to...? to ask about obligation.

Leçons associées

• Modal verbs
• Modal verbs
• Modal verbs