• If you are citizen of an European Union member nation, you may not use this service unless you are at least 16 years old.

  • You already know Dokkio is an AI-powered assistant to organize & manage your digital files & messages. Very soon, Dokkio will support Outlook as well as One Drive. Check it out today!



Page history last edited by Béatrice H. Alves 14 years, 3 months ago


* MODALS (not including Conditional Sentences)


They allow to say that something has to be done or is advisable or forbidden; or, like a rheostat, they enable you to express a whole range of nuances from certainty to doubt or impossibility.






Modals are used to express many attitudes to events.  The main areas are:

-         Probability: when we want to say how certain we are that something will happen (e.g. may, might, should)

-         Obligation: when we want to say that something will definitely happen because the situation demand it (e.g. must, have to); or to say that it is desirable or ‘correct’ for something to happen (e.g. should, ought to)

-         Necessity: when we say that something is or is not necessary or useful (e.g. need(n’t), need to)

-         Ability / success: to say that something is possible (e.g. can), or that an action was successful (was able to)

-         Permission: to ask whether (or to say that) something is allowed (e.g. may, might, can, could)

-         Condition: when we want to say that one action depends on another (i.e. if sentences – not covered here but check there)



On this page, you’ll find a description of the main, common uses of modals. Modals are subject to changes of fashion

(e.g. That’s got to be Simon for That must be Simon)

and social or regional preferences

(e.g. Have we to? Have we got to? or Do we have to?).

So be prepared to hear or read variations.








The most common modals are:

will - would - shall - should - can - could - may - might - must - ought to



Their common most important features are:

-         They take the same form in all persons. There is no –s ending in the third person singular present. (She cans fix it --> She can fix it.)

-         After all modals (except ought) we use the base form of the main verb without to. (I must to study.  --> I must study.)

-         We don’t use two modals together. (I will can evaluate it. --> I will be able to evaluate it.)

-         We don’t use modals with other auxiliaries. (Do you must turn it on? --> Must you turn it on?)

-         A same modal can express different attitudes according to context. (You may use this runway. = authorization – You may have a hydraulic failure. = Probability)





We form the affirmative by putting the modal verb between the subject and the base form of the main verb.



He can fly.

We should hold a meeting. 


We form the negative by adding n’t/not after the modal.


He can’t fly.

We shouldn’t hold a meeting.


We form the interrogative by inverting the subject and the modal.



Can he fly?

Should we hold a meeting?


We can also form questions or ask for confirmation by using tag questions.



He can fly, can’t he?

We shouldn’t hold a meeting, should we?


We can use the structure modal + be + ing.



He must be landing right now.

We may be working late tomorrow.


We can use the structure modal + have + past participle to refer to the past.



He must have forgotten to read the checklist.

We may have misunderstood the instructions.


We use the structure modal + be + past participle to give a present passive meaning.



Our flight may be delayed by the local authorities.

The switches must be turned off.


We use the structure modal + have + been + past participle to give a past passive meaning.



Passengers should have been transferred to the terminal.

These chemicals might not have been stored properly.


Back to top






Possibility and Probability: may, might, could, should, must, will




Possibility: may, might, could

We use may, might and could to talk about present or future possibility.

Might is normally a little less sure than may. Could is normally less sure than may or might.

+++ may        ++ might    + could

We’re looking for any physical signs that could show that someone is nervous or angry – signs that they might be planning a criminal act.

If they detect behavior that indicates a person may be a threat to security or the safety of a flight, they attempt to engage in casual conversation with that person. 


Back to top


Probability: should, ought to

We can use should or ought to to say that something is probable at the moment of speaking, or in the future.

She should be in the patio by now. (She is probably in the patio; she landed 30 minutes ago.)

I should finish work early today. I haven’t got much to do. (= I will probably finish work early today.)

He ought to get his license easily. He’s a very good pilot. (=He will probably get his license easily.)



We use should have / ought to have + past participle when we expected something to happen and we don’t know if it did, or if we now know it didn’t.

They should have arrived by now. (The supplier promised them for this morning but I haven’t checked if they have arrived.)

He should have gotten his license easily. I’m surprised he failed.


Back to top



Deduction: must, can’t

We use must in deductions to say that we are sure about something.

He must know the route very well. He has done it more than a hundred times. (=I’m sure he knows the route very well.)

If people show multiple signs of stress, then you can assume that they must have something to hide.

He must have gone to the paint shop. His shoes are all blue. (= I’m sure he went to the paint shop.)



We use can’t in deductions to say that something is impossible.

The tanks can’t be empty. We filled them up at the last stop. (=It’s impossible that they be empty.)

You can’t have talked to our US manager yesterday. It was a holiday there. (=It is impossible that you talked to him.)

Surely friendly conversations can’t be enough to indicate if a passenger is a criminal.


Back to top


Predictions and Expectations: will, may, might

We use will to talk about future developments that we are certain about, and should for more immediate expectations.

One sensor will stop the first-officer falling asleep.

Traffic congestion will not be an easy problem to solve.

How will the car of the future be powered?

The fuel hoses should be working properly.

The warning light shouldn’t be flashing.



We use may and might when we are less certain about future developments, i.e. when we think that something is possible rather than definite. There is little difference between may and might.

A hybrid car may be the best choice.

A noise-free bike might not be popular with bikers.

Might hydrogen fuel cells get cheaper?

Back to top



Ability: can, could, be (un)able to

We use can to talk about present ability, to say what someone knows how to do, or what is possible. Could is the past form of can to express the same idea.. To talk about future abilities and whenever it’s impossible to use a modal, we use be able to or be unable to. Eventually, when we want to say that someone had the ability to do something, and that they did it in a particular situation, we can use manage to (+base) or succeed in (+ing).

Now we can fly nonstop around the world. A century ago we couldn’t do such thing. But 50 years from now, we’ll be able to get to outer space without even flying.

We couldn’t reach the chief engineer because he was on vacation but she managed to speak to him anyway.

We will be unable to land on such a runway.

Back to top



Obligation and necessity: must, have to, have got to, should

We use both must and have to to express obligation or necessity, but there is sometimes a difference between them.


* Must expresses a strong obligation, usually dictated by some kind of authority, when you have no choice.

You must wear a safety helmet.

Eye protection must be worn.

You must declare dangerous goods.


* Have to (and eventually have got to, which is more informal) expresses an obligation or a necessity, usually dictated by circumstances or external rules, when you have a choice.

We have to reduce our fuel consumption.

I have to wear glasses to watch TV.

Sensors have to be checked every week.

Do we have to wear safety equipment here?


* Must has no past, no infinitive, no -ing form and no participles. So, when necessary, we make these forms with have to.

I had to work late yesterday. (I musted work late…)

I’ll have to work late tomorrow (I’ll must work late…)

He hates having to work late. (He hates musting….)

He has had to work hard all his life. (He has musted work….)


* Should and ought to express an obligation when you are free to do or not to do such things.

I should report this incident to the boss.

Should I stay?

You should always wash your hands after using this product.


Back to top



Prohibition and negative necessity

We use mustn’t to express a prohibition and when it’s necessary that we not do something.

Unauthorized persons must not cross this line.

Hand luggage to be taken into the cabin mustn’t contain any dangerous or flammable items.

I mustn’t forget my next health check.


Back to top



Advice, opinion and suggestion: should, ought to, can, may

We use should, ought to and should not (shouldn’t) to give advice, to offer an opinion, or to ask for those. It’s also possible to use may and can to make less direct suggestions.

You should keep your password safe.

People shouldn’t take sleeping pills before flying.

Who should I complain to?

You may want to move the patient to the rear of the plane.

It can help to walk around the cabin during the flight.


Back to top



Orders and requests: can, could, may, will, would

When giving orders, expressing requests, or asking for favors, the choice between can, could, may, will and would depends on how polite and imperative one wants to be.

Could is less direct and more polite than can. May is more formal than can and could. Will is less polite than would and can show some irritation.

Can you find a fire extinguisher, please?

Could you exit the runway, please?

May I have the last update on this, please?

Would you bring me some water, please?

Put on your mask, would you?

Will you please stop spilling oil everywhere?


Back to top



Permission: can, could, may, might, be allowed to

When asking for permission, the choice between can, could, may and might depends on how polite and direct one wants to be. Whenever the use of a modal is impossible, we can use be allowed to.

Could is less direct and more polite than can. May is more formal than can or could. Might is even less direct and more formal.

Can I send you an email to confirm our deal?

Could we unlock the guillotine now?

Most passengers know what they may and may not bring on board.

Might I make a suggestion?


Back to top



More hints and practice about modals on the Modals Plus page.




  1. From Students' English Grammar by Jake Allsop / Cassel Publishers Limited - ISBN 0.304.30532.4

Comments (0)

You don't have permission to comment on this page.