Modal Verbs in English Grammar

Introduction

The modal verbs in English grammar are can, could, may, might, must, need not, shall/will, should/ought to. They express things like ability, permission, possibility, obligation etc. Modal verbs only have one form. They do not take -s in the simple present and they do not have a past simple or past participle form. However, some modal verbs have alternative forms which allow us to express the same ideas in different tenses.

Learn about the usage of modal verbs and their alternative forms in English grammar with Lingolia’s online lesson. Then put your knowledge to the test in the interactive exercises.

Example

Max’s father is a mechanic. He might retire soon, so he thinks Max should work in the garage more often.

Max can already change tyres, but he has to learn a lot more about cars.

Max must do what he is told and must not touch any dangerous equipment.

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Conjugation of English Modal Verbs

There are a few point to consider when using modal verbs in a sentence:

  • Modal verbs are generally only used in the present tense in English but we don’t add an -s in the third person singular.
    Example:
    He must do what he is told.
    (not: He musts …)
  • Modal verbs do not take an auxiliary verb in negative sentences and questions.

    Example:
    Max need not worry about his future.
    Max must not touch any dangerous equipment.
    Can Max change a tyre?
  • We always use modal verbs with a main verb (except for short answers and question tags). The main verb is used in the infinitive without to.
    Example:
    Max can change tyres.
    (not: Max can to change tyres.)

Usage

We use modal verbs to express ability, to give advice, to ask for and give permission, to express obligation, to express posibility, to deduce and to make predicitions.

Can/Could for Ability

modal verb alternative form
can/could to be able to

We use can in simple present.

Example:
Max can already change a tyre.

We can use the alternative form to be able to in all tenses (present, past, perfect, progressive and future).

Example:
In two years time, Max will be able to do everything in the garage.

We use could or the alternative form was/were able to in simple past.

  • We use could for general ability and with the verbs feel, hear, see, smell, taste, remember and understand.
    Example:
    Max’s father could do everything in the garage.
    Max’s father could remember changing his first tyre.
  • We use was/were able to when we talk about something specific in the past.
    Example:
    Was Max able to change the tyre yesterday?

To Note

There is no difference between the negative forms couldn’t and wasn’t/weren’t able to.

Example:
Max’s father couldn’t work in the garage alone.
Max’s father wasn’t able to work in the garage alone.

Should/Ought to for Advice

We use should/ought to to give advice, make suggestions or say what is a good idea.

Example:
Max should/ought to work more often in the garage.

To make suggestions about something that has already happened we use should/ought to + have + past participle.

Example:
Max shouldn’t/ought not to have played computer games all day.

Can/could/may/might for Permission

modal verb alternative form
can/could/may/might be allowed to

We use can/could/may/might to ask permission in simple present. Could is more polite than can, and may/might is more polite than could.

Example:
Can/Could/May I leave my car here for repairs?

We usually only use may in questions with I and we.

We only use can or may, but not could, to give permission.

Example:
Max, you can/may change this tyre.

We use could in conditional clauses and in simple past.

Example:
Max could change the tyre if he wanted to.
Max could/was allowed to leave early yesterday.

We can use be allowed to in all tenses.

Example:
Max will be allowed to use the dangerous equipment soon.

Must/need not/should for Obligation

modal verb alternative form
must have to
mustn’t be not allowed to
need not don’t have to
should/ought to be supposed to/be expected to

We use must to say what is necessary and give orders or advice in a strong way. With must, the obligation is usually imposed by the speaker.

Example:
His father says, “You must do what you are told.”

We use have to when the obligation is general (e.g. a rule or law), or we are expressing past or future obligation.

Example:
Max is only 12 so he has to go to school.
Max’s father had to go to school too.

We use mustn’t/be not allowed to to say what is not allowed or forbidden.

Example:
Max mustn’t/isn’t allowed to touch any dangerous equiptment.

We can use should/be expected to like must but it is weaker.

Example:
Max should/is expected to study hard.

We use need not/don’t have to when there is no obligation.

Example:
Max need not/doesn’t have to worry about his future.

May/might for Possibility

We use may/might to express possibilty in the future. There is no difference in meaning between may and might. We don’t usually use contractions with may not and might not.

Example:
Max’s father might retire soon.
Max may not take over his father’s garage.

May/can’t/must/will/shall for Deduction

  • We use may/might when we think something is perhaps true, but we are not 100% sure.
    Example:
    Max may/might not want to work in the garage forever.
    We can replace may/might with could in positive sentences, but not with can.
    Example:
    Max’s father may/might/could retire soon, he is almost 60.
    To speculate about something in the past we use may/might (not) + have + past participle.
    Example:
    Max’s grandfather may/might have wanted to retire when he was 50.
  • We use can’t to express something we are sure is untrue or impossible in the present.
    Example:
    Max can’t be retired, he’s 12 years old. (but not: Max mustn’t be retired.)
  • We use must to express something we are 100% sure is true in the present.
    Example:
    Max’s grandfather must be retired, he’s 90 years old. (but not: Max’s grandfather can be retired.)
    To speculate about something in the past we use can’t/must + have + past participle.
    Example:
    Max’s father must have worked very hard.
  • We use will (not)/shall (not) when we make a predicition about the future, or when we are sure about something in the future.
    Example:
    The car won’t/shan’t be ready tomorrow.
    Max will/shall be a wonderful mechanic.

Offers/Requests

We can often choose between two modal verbs with similar meanings when we ask questions or make requests. One form is more polite than the other.

Normal FormPolite FormExample
can (ability) could Can you repair this flat tyre?
Could you repair this flat tyre?
can (permission) may/might Can we come in?
May/might we come in?
shall* should Shall he pick the car up tomorrow?
Should he pick the car up tomorrow?
will* would Will the car be ready tomorrow?
Would the car be ready tomorrow?

*Will/Shall

We use will to make requests/ask somebody to do something. When we want to make a suggestion using the interrogative form in the 1st person (I, we), we use shall.

Example:
Max, will you change that tyre?
Change the tyre, will you?
Shall I change that tyre?

Alternative Forms

If we want to indicate a situation in the past, we have to use the alternative forms instead of the regular modal verbs. The list below provides an overview of modal verbs and their alternative forms, along with examples.

Example

Max’s father took over the garage from his father. He did not have to worry about his future either. Max’s father also had to learn a lot and had to do what he was told. He was not allowed to touch dangerous equipment. He was expected to work in the garage often. However, Max’s father was not as talented as Max and was not able to change tyres until he was 15 years old.

List – Modal Verbs and Alternative Forms

modal verbalternative formexample sentence
must to have to Max must do what he is told.
His father also had to do what he was told.
must not not to be allowed to
Max must not touch anything dangerous.
His father was not allowed to touch anything dangerous.
can (ability) to be able to/
could*
Max can already change tyres.
His father was not able to/couldn’t change tyres.
can (permission) to be allowed to/
could*
Max can help in the garage at the age of 12.
Max’s father was allowed to help at the age of 13.
need not not to have to Max need not worry about his future.
Max’s father did not have to worry about his future either.
should/ought to to be supposed to/to be expected to/to be to Max should work in the garage more often.
Max’s father also was supposed to/was expected to/was to work in the garage often.

Of course, we can also use the alternative forms (except for could) in other tenses.

Example:
Max can change tyres. = Max is able to change tyres.

* We use could and was/were able for the past of can. We use could for general ability and with the verbs feel, hear, see, smell, taste, remember and understand. We use was/were able to when we talk about something specific in the past. The negative couldn’t can be used in all three cases.

Example:
Max’s father could do everything in the garage.
Max’s father could remember changing his first tyre.
Was Max able to change the tyre yesterday?
Max’s father couldn’t work in the garage alone.