Rules of the Game: Must, Have to, Should and Mustn't

Les clés de la leçon

Mot	Traduction
modal verbs	verbes modaux
must	devoir (obligation)
mustn't	ne pas devoir (interdiction)
have to	devoir (obligation externe)
should	devoir (conseil)

Imagine your first day at a British school. On the wall, a big poster says: "You must wear your uniform. You mustn't use your phone in class. You should raise your hand to speak." Rules, rules, rules! Every place — school, the street, a swimming pool — has them. And in English, we have special little words called modal verbs to talk about what you have to do, what you mustn't do, and what you should do. Let's crack the code!

1. Must and Have to: expressing obligation

Both must and have to mean "il faut", "c'est obligatoire". They express an obligation.

• You must arrive on time. → Tu dois arriver à l'heure.
• Students have to wear a uniform. → Les élèves doivent porter un uniforme.

! Notice the grammar!

• After must, the verb stays in the base form (no to, no -s): He must study. (never He must to study)
• Have to changes with the subject: I have to, but he/she/it has to: She has to leave.

→ Small nuance: must often sounds like a personal or strong rule (the speaker decides), while have to sounds like a rule that comes from outside (a law, the school).

• I must call my grandma. (I decide it's important.)
• We have to stop at a red light. (It's the law.)

2. Mustn't: expressing prohibition

Mustn't (= must not) means "il ne faut pas", "c'est interdit". It's a prohibition.

• You mustn't run in the corridor. → Tu ne dois pas courir dans le couloir.
• We mustn't be late. → Nous ne devons pas être en retard.

! Careful! Mustn't is NOT the opposite of must in French. It means "c'est interdit", not "ce n'est pas obligatoire". To say something is not necessary, you use don't have to:

• You mustn't smoke here. → interdit ✗
• You don't have to come. → tu n'es pas obligé (mais tu peux) ✓

3. Should: giving advice

Should means "tu devrais", "il faudrait". It gives a piece of advice — softer than an obligation!

• You should drink more water. → Tu devrais boire plus d'eau.
• You shouldn't shout at people. → Tu ne devrais pas crier sur les gens.

Like must, should is followed by the base form: She should rest.

À retenir

• Must / have to = obligation (il faut). After must: base verb. Have to → has to (he/she/it).
• Mustn't = interdiction (c'est interdit), NOT "pas obligatoire".
• Don't have to = ce n'est pas obligatoire (mais tu peux).
• Should / shouldn't = conseil (tu devrais / tu ne devrais pas).
• Modal verbs (must, should) never take to and never take -s.

★ Pour aller plus loin

In everyday English, people often prefer have to over must, especially in spoken language and in the past or future — because must has no past form! You can't say "I musted". Instead you use had to: Yesterday I had to stay home. And for the future: I'll have to work tomorrow.

There's also a polite cousin of should called ought to ("tu ferais bien de"). You ought to apologise. It means almost the same as should, but it sounds a bit more formal and old-fashioned — you'll spot it in books more than in the playground.

Finally, watch out for British signs! In the UK you'll read "You must not feed the animals" at the zoo, or "Passengers must not lean out of the window" on trains. Spotting real modal verbs in the wild is a great way to remember them — the whole English-speaking world is a giant grammar exercise!

Sources pour creuser

Livres :

• English Grammar in Use de Raymond Murphy (Cambridge) — les chapitres sur must / have to / should sont clairs et pleins d'exemples.
• Harrap's Grammaire anglaise (collection Harrap's) — une grammaire simple adaptée aux collégiens.

Vidéos / chaînes YouTube :

• Chaîne « ISpeakSpoken » — cherche « must have to should anglais » : explications en français.
• Chaîne « Anglais avec Sophie » — cherche « modaux anglais must should ».
• Chaîne « Lingua.com » ou « BBC Learning English » (en anglais) — cherche « modals of obligation ».

Ressources institutionnelles :

• lumni.fr — rubrique Anglais collège : cherche « exprimer l'obligation en anglais ».
• education.gouv.fr — programmes officiels de langues vivantes au cycle 4.

Mots à retenir

• rule : règle
• must : devoir (obligation stricte)
• allow : permettre
• obligation : obligation (responsabilité)
• forbidden : interdit, défendu