Grammaire anglaise

Les verbes modaux d'obligation

LES VERBES MODAUX, Seconde partie

must, have to, should et ought to

En anglais il existe deux sortes de verbes modaux d'obligation ; ceux qui expriment essentiellement une obligation ferme ou une nécessité - must et have to - et ceux qui expriment une recommandation ou obligation morale - should et ought to . On peut aussi considérer comme verbe modal need (to), qui exprime différentes valeurs d'obligation selon le contexte.

Obligation ferme, etc. - must et have to

Le verbe must n'existe qu'aux formes du présent simple et du present perfect.
Tandis que la forme du présent peut exprimer une obligation, une nécessité, une certitude ou une probabilité forte, la forme du present perfect ne sert qu'à exprimer un avis ou une supposition forte.

Toutes personnes	présent	présent perfect
affirmatif	must	must have
négatif	must not, mustn't	must not have, mustn't have

Si d'autres temps sont requis, le locuteur doit avoir recours au verbe modal synonyme de must "have to" . Cet auxiliaire modal, suivi de l'infinitif avec to, a tous les temps requis, y compris les formes progressives. Ces dernières sont rares, mais ont le mérite d'exister .

Temps principaux	présent	présent perfect	Passé	Futur
affirmatif:	has to, have to	has had to have had to	had to	will have to
négatif;	does not have to, do not have to , doesn't have to don't have to	has not had to have not had to	did not have to didn't have to *	will not have to won't have to
Progressive ou continuous	am having to is having to, are having to	has been having to have been having to	was having to were having to	will be having to

* La forme "had not to" existe aussi, mais elle est rare et considérée comme archaïque.
A l'oral, et uniquement au temps présent, have to est souvent consolidé par l'addition du mot got; c'est-à-dire qu'au lieu de dire I have to on dira souvent I've got to.
Pour d'autres usages de have, voir Le verbe have

Must et have to s'emploient pour exprimer:
a. Une obligation forte ou une nécessité
b. Une certitude ou une probabilité forte.
c. Must have exprime une supposition.

Exemples:

a1) You must leave immediately !
a2) I have to get up early on Wednesday. I've got an exam !
a3) You mustn't park their car there, it's blocking the entrance.
a4) I had to go to the dentist, because I had broken a tooth.
a5) I had to wait outside in the rain ! I lost my key !
a6) The boss is away today; he's had to go to London to see a client.
a7) On Sunday it's going to snow; we'll have to change our plans.
a8) I'm having to move because I've got a new job in Brighton.
a9) That's great! But you didn't have to pack all the books into boxes !

b1) You must be over a hundred, if you were born in 1915.
b2) If my sister's not in Liverpool, she has to be in Brighton.
b3) I've got no mistakes, so I must be one of the winners !
b4) If I 'm not mistaken, it has to be somewhere in this room.

c1) I can't see my book, I must have left it at school.
c2) If they're still at the beach, they mustn't have heard the news.

Attention !
Comprenez la différence entre "had to" et "must have"

They had to go to Liverpool
= Ils ont été obligés d'aller à Liverpool.
They must have gone to Liverpool.
= A mon avis, ils ont dû aller à Liverpool.

Recommendation ou obligation morale - should et ought to

Le verbe should n'existe qu'aux formes du présent et du present perfect .
Formes de should

Toutes personnes	présent	présent perfect
affirmatif	should	should have
négatif	should not, shouldn't	should not have, shouldn't have

Le verbe ought to n'existe qu'aux formes du présent et du present perfect .
Formes de ought to

Toutes personnes	présent	présent perfect
affirmatif	ought to	ought to have
négatif	ought not to, oughtn't to	ought not to have, oughtn't to have

Should et ought to sont synonymes.

Exemples:

1) You should stop drinking so much whisky !
2) It's after ten o'clock, the children ought to be in bed by now.
3) I didn't know you were from Bristol ! You ought to have told me !
4) If you'd wanted to get a good job, you should have worked harder at school.
5) That jacket's dirty, you should get it cleaned.
6) That jacket's dirty, you ought to get it cleaned.
7) That's terrible ! He really oughtn't to have told them about it.

Need (to)

Le verbe need peut être utilisé comme verbe modal. Utilisé comme verbe modal (suivi d'un autre verbe) il exprime différentes degrés d'obligation selon le contexte .
Au négatif il exprime une absence d'obligation. La version contractee needn't n'est jamais suivi de to.

Formes de need

Toutes personnes	présent	past	présent perfect
affirmatif	need	needed	(à éviter)
négatif	don't need ou needn't	didn't need	need not have, needn't have

Exemples:

1) You need to see a doctor !
2) I needed to get up at 6, so I could revise before the exam.
3) I don't need to take any medicine since I'm not ill.
4) I didn't need to take any medicine since I wasn't ill.
5) Oh that's so kind of you, but you needn't have been so generous.
6) The president need not have resigned, as he had not done anything wrong.

► Autres verbes modaux: Modaux de possibilité; can, may etc.

► Autres verbes modaux: Modaux de futurité - will, shall etc.

► Autres verbes modaux: Modaux d'habitude passée - would, used to.