Master Must, Have To, and Can: B1 Modal Verbs for Obligation and Permission — B1 English grammar lesson by Langcom

Master Must, Have To, and Can: B1 Modal Verbs for Obligation and Permission

Raúl Maguiña

Gründer von Langcom | Prüfer für Cambridge- und SIELE-Prüfungen

September 6, 2026

B1✏️ Grammatik⏱️ 6 min read
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Must, have to, und can are modal verbs that help us talk about obligation, necessity, and permission in English. While they might seem similar, their meanings and uses are distinct. Must expresses a strong, often internal, obligation or a strict rule, like You must wear a seatbelt. Have to indicates an external obligation or a general necessity, such as I have to work tomorrow. Can is used for permission or ability, as in You can leave now. Understanding these differences is crucial for clear communication at a B1 level. Pay close attention to their negative forms, as mustn’t und don’t have to have very different meanings.

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.

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When Do We Use “Must”?

Wir verwenden 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?

Wir verwenden 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 (z. B., She must leave now.)
    Subject + have to / has to + base verb (z. B., They have to study. / He has to work.)
    Subject + can + base verb (z. B., We can go.)
  • Negative:
    Subject + mustn't + base verb (z. B., You mustn't talk.)
    Subject + don't have to / doesn't have to + base verb (z. B., I don't have to cook. / She doesn't have to pay.)
    Subject + can't + base verb (z. B., 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 und have to have very different meanings.

  • Mustn't (oder 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 (oder 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.

  • Für have to: Verwendung Do oder Does.
    Do I have to bring my passport?
    Does she have to work on weekends?
  • Für can: Invert the subject and can.
    Can I open the window?
    Can they speak French?
Summary of Must, Have To, and Can
Modal Verb Bedeutung Negativform Beispiel
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.

Beispiele

  • 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.

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Häufige Fehler bei Spanischsprechern

Spanish speakers often make these mistakes:

  • Verwendung von 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.
  • Verwirrend mustn't und 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: Denken Sie daran, dass have to Änderungen an has to for third-person singular subjects (he, she, it).
    Incorrect: He have to study.
    Correct: He has to study.

Häufig gestellte Fragen

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?

Nein, must does not have a past form. For past obligations, we use had to. Zum Beispiel:, 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 (z. B., Must I go?) sounds very formal or old-fashioned. We typically use Do I have to...? oder Is it necessary to...? to ask about obligation.

Verwandte Lektionen

Über den Autor: Raúl Maguiña

Raúl Maguiña ist Leiter der Asociación Educativa Langcom, einem autorisierten Cambridge English-Vorbereitungszentrum in Ihr Land. Mit mehr als einem Jahrzehnt Erfahrung in der Sprachausbildung und der internationalen Zertifizierung hat er Tausenden von Schülern, Lehrern und Bildungseinrichtungen in 25 Ländern zu Cambridge-, IELTS-, TOEFL- und Michigan-Englischzertifikaten verholfen.

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