Anglais

Modal Verb: Nine Words That Set the Level of Certainty

Modal verbs change how certain or how obliged a sentence sounds. The nine core modals ranked, one sentence written at three strengths, and how they behave.

Modal verb

A modal verb is a helping verb such as must, should or might that shows how certain, possible, permitted or obligatory the main verb's action is.

Aussi appelé: Modal auxiliary, Modal auxiliary verb
Où les élèves le rencontrent: Grade 5 English; the national curriculum for England introduces modal verbs in Year 5 as one of the ways of indicating degrees of possibility.

La réponse en bref
A modal verb sits in front of another verb to show how certain, possible or obligatory something is. The nine core modals are can, could, may, might, must, shall, should, will and would. You must hand it in and you could hand it in describe the same act at opposite strengths.

Un exemple

You must hand it in tomorrow. / You should hand it in tomorrow. / You could hand it in tomorrow.

One word changes and the instruction changes completely. Must removes the choice. Should recommends and leaves the choice in place, which is why it is both the polite version and the ignorable one. Could offers tomorrow as one option among several and applies no pressure at all. A student who can move between those three has most of what politeness in written English requires.

The nine, and the near-modals

Nine verbs make up the core group, and they behave as a set rather than as nine separate words.

can, could — ability and possibility
may, might — possibility and permission
must — obligation, and strong deduction
shall, should — obligation and expectation
will, would — certainty, prediction and the conditional

Ranking them by certainty

A handful of other verbs do the same job without behaving quite the same way: ought to, need, dare and used to. They are usually called semi-modals or marginal modals, and a school answer that names them as modal verbs is unlikely to be marked wrong.

Take one sentence about the weather and change only the modal. What comes out is a ladder from near-certainty down to bare possibility.

It will rain. — Stated as a fact about the future.
It must be raining. — A deduction: the evidence leaves no other explanation.
It should rain later. — Expected, on the basis of what is normal or forecast.
It may rain. / It might rain. — Possible. Might is generally read as slightly less likely than may.
It could rain. — Possible in principle, with no view offered on how likely.
It can't be raining. — A deduction in the negative: the evidence rules it out.

How modal verbs behave differently from every other verb

Notice that must and can't are the deduction pair in that list, not the obligation pair. The same nine words run two ladders at once — one for how certain something is, one for how strongly it is required — and which ladder is in play is decided by the sentence rather than by the word.

The group is also identifiable by grammar alone, which is more reliable than identifying it by meaning:

No -s in the third person. He must go, not he musts go.
No to after them. She might come, not she might to come.
No infinitive and no participle. There is no to must and no musting.
Questions by inversion. Must I? not do I must?
They do not stack. She will can swim is impossible; English says she will be able to swim.

Core modal verbs in English, before the semi-modals are counted: 9Core modal verbs in English, before the semi-modals are counted

Questions fréquentes

What are the nine modal verbs?

Can, could, may, might, must, shall, should, will and would. Some lists add ought to, need, dare and used to, which behave similarly but not identically and are usually called semi-modals. The core nine are the ones that follow every grammatical rule of the group without exception.

What is the difference between may and might?

Both express possibility, and in most sentences they are interchangeable. Might reads as marginally less likely, and it is the safer choice for something that did not in fact happen — we might have missed it rather than we may have missed it. May is also the more formal word when the meaning is permission.

Is should the same as must?

No, and confusing them changes how an instruction reads. Must states an obligation with no choice attached; should gives advice and leaves the decision with the reader. In formal writing this matters, because a rule written with should is a recommendation and readers will treat it as one.

Why do modal verbs matter in writing tasks?

Because they set the tone of a piece almost single-handedly. A persuasive letter written entirely with must sounds like a demand; the same letter with should and could sounds reasonable. Mark schemes for persuasive and formal writing reward that control, and modal verbs are the quickest lever a student has on it.

Sources

National curriculum in England: English programmes of study — Department for Education

Dernière mise à jour 21 août 2026