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Modal verbs

Level: beginner

The modal verbs are: 



We use modals to show if we believe something is certain, possible or impossible:

My keys must be in the car.
It might rain tomorrow.
That can't be Peter's coat. It's too small.

We also use them to do things like talk about ability, ask permission, and make requests and offers:

I can't swim.
May I ask a question?
Could I have some tea, please?
Would you like some help?

Modal verbs




Good day!

In this section, I`ve read that COULDN`T is the negative form of MUST.

In another source, it says CAN`T can also be a negative form of the same modal verb.

May I know the difference? When are COULDN`T and CAN`T used?

Thank you very much!

Hello Timmy Ferrer,

Modal verbs have multiple uses and there is no one-to-one correlation between them in terms of which modal is used to express the negative meaning of another verb. The opposite of must in one context might be can't; in another it might be mustn't; in another it might be don't have to.

If you want to check whether two modals have opposite meanings then we'll be happy to help, but you need to put the modals into sentences so we can see which use is relevant.



The LearnEnglish Team

Thank you so much for your reply.

How about these examples?

1. You mustn't wear casual clothes at work.
2. You can't wear casual clothes at work.
3. You don't have to wear casual clothes at work.

Thank you, once again, in advance!

Hello again Timmy,

It's important to distinguish between the grammatical negative, which is simply the addition of 'not' to the modal verb, and expression of the opposite meaning, which may be expressed by grammatical negation or may require a different modal verb. My answers below describe the most likely options for expressing the opposite meaning.

1. The opposite of mustn't wear (negative obligation) could be must wear (positive obligation) or don't have to wear (lack of obligation).

2. The opposite of can't wear (no permission or no ability) could be may wear (permission) or can wear (permission or ability).

3. See my answer to 1 above. You could also use have to wear here with a similar meaning to must wear.



The LearnEnglish Team

Candidates may not bring calculators into the examination room. - How is it different from "must not" or "shall not"?

And is there any difference between might, may, could when it comes to present/future possibility?

Hello Sunyoung1005,

You can express prohibition in various ways in English: may not, can not, are not allowed to, shall not, should not, must not can all express prohibition. There may be preferences of style or preferences dependent on particular contexts, but all are possible.


Could, might and may are all used to express present/future possibility and I don't think there are any distinctions between them.



The LearnEnglish Team

Hello! I have 3 questions:

Question 1) To make the statement “I’m no angel” true, it is neither not necessary nor sufficient that I should not be a member of the set of angels. ---- Why is the meaning of "should" here?

Question 2) If it rained last night the match will have been cancelled. ---- How is it different from "must"?

Question 3) According to a grammar book, to make confident predictions about the present based on our knowledge or experience, we use will/won’t: It is five o’clock. Janet will be in Paris now (the speaker believes it is true). ---- My question is whether I could we use “must” instead? Is there any difference in meaning?

Hello LilyLinSZ,

1) This use of should is a variant on the present subjunctive, used for expressing things that we wish for, assume or imagine. You can read more about the subjunctive in English here:


2) In this sentence, will expresses a firm belief or certain knowledge; must expresses a strong expectation based on existing knowledge, deduction or experience. Will expresses certainty on the part of the speaker; must expresses strong expectation, but is still speculative.


3) The explanation here is the same as for the second question. Both will and must are possible, with the differences in meaning noted above. You could also use might, may, could and should). If you change by now to yet then the negative forms of the modals are also possible.



The LearnEnglish Team

Hi Teacher,

I hope you are doing great!

Your secretary told me that you would be coming over. Otherwise I should have felt compelled to call you at home - Why is "should have felt..." used instead of "would have felt..."

I reluctantly agreed to a postponement on condition that the sale should be completed and the boat handed over by 31st August.

Is the use of 'should' here considered a past tense form of "shall"?

Hi hyunjoo76,

In the first example, using should sounds more formal or official in style than would

For the second example, yes! Should here has the meaning of shall in the past tense. It's another example of should to make a statement sound official.

Does that make sense?

Best wishes,


The LearnEnglish Team