The modal verbs are can, could, may, might, mustshall, should, will and would.

The modals are used to do things like talking about ability, asking permission making requests, and so on.

Ability:

We use can to talk about someone’s skill or general abilities:

She can speak several languages.
He can swim like a fish.
They can’t dance very well.

We use can to talk about the ability to do something at a given time in the present or future:

You can make a lot of money if you are lucky.
Help. I can’t breathe.
They can run but they can’t hide.

We use could to talk about past time:

She could speak several languages.
They couldn’t dance very well.

We use could have to say that someone had the ability/opportunity to do something, but did not do it:

She could have learned Swahili, but she didn’t have time.
I could have danced all night [but didn't].

Permission:

We use can to ask for permission to do something:

Can I ask a question, please?
Can we go home now?

could is more formal and polite than can:

Could I ask a question please?
Could we go home now?

may is another more formal and polite way of asking for permission:

May I ask a question please?
May we go home now?

We use can to give permission:

You can go home now if you like.
You can borrow my pen if you like.

may is a more formal and polite way of giving permission:

You may go home now, if you like.

We use can to say that someone has permission to do something:

We can go out whenever we want.
Students can travel free.

may is a more formal and polite way of saying that someone has permission:

Students may travel free.

Instructions and requests:

We use could you and would you as polite ways of telling or asking someone to do something:

Could you take a message please?
Would you carry this for me please?
Could I have my bill please?

can and will are less polite:

Can you take a message please?
Will you carry this for me please?

Suggestions and advice:

We use should to make suggestions and give advice:

You should send an email.
We should go by train.

We use could to make suggestions:

We could meet at the weekend.
You could eat out tonight.

We use conditionals to give advice:

Dan will help you if you ask him.

Past tenses are more polite:

Dan would help you if you asked him.

Offers and invitations:

We use can I… and to make offers:

Can I help you?
Can I do that for you?

We can also use shall I …

Shall I help you with that?
Shall I call you on your mobile?

We sometime say I can ... or I could ... or I’ll (I will) ... to make an offer:

I can do that for you if you like.
I can give you a lift to the station.
I’ll do that for you if you like.
I’ll give you a lift to the station.

We use would you like (to) ... for invitations:

Would you like to come round tomorrow?
Would you like another drink?

We use you must or we must for a very polite invitation:

You must come round and see us.
We must meet again soon.

Obligation and necessity

We use must to say that it is necessary to do something:

You must stop at a red light.
Everyone must bring something to eat.
You can wear what you like, but you must look neat and tidy.
I’m sorry, but you mustn’t make a noise in here.

We use had to for this if we are talking about the past:

Everyone had to bring something to eat.
We could wear what we liked, but we had to look neat and tidy.
 

Exercise

Section: 

Comments

Thank you for such useful piece of grammar!
But.... i don't quite understand when we use "must" and when "have to" (in Present tenses)?

 Hi Olessya

I think (and not everyone agrees) that must expresses both obligation and authority.

Have to expresses obligation but the authority, or reason for the obligation comes from somewhere else.

When I was a child, the main authority figures in my life were my parents and they would say things like: "You must tidy your room!" Or: "You must work hard at school!" If I ever asked why, the answer was simply: "Because I said so!"

Must is for people in authority.

Teacher - student: You must do your homework.

Doctor - patient: You must eat more vegetables.

Expert - novice: You must listen very carefully.

I think you have to be careful when you use must because it can make people uncomfortable. If someone tells me to do something using must who is not an authority, a little voice in my head rebels and shouts "You're not my mum!"

Have to doesn't express authority. The authority comes from somewhere else.

In the UK, you have to wear a seatbelt in a car. Authority = it's the law.

When you are in the cinema, you have to turn off your mobile phone. Authority = cinema rules.

Sometimes, we use logic or reason as an authority. 

You have to put petrol in your car, not diesel. Authority = common sense (if you don't, it won't work)

Here's an example I use with my students:

I come from London so I know a lot about London. If one of my students is going to visit the UK, I might tell them: "Oh, you must visit the National Gallery."

I can say this because I've been there. I have never been to New York so if one of my friends is going to visit, I might say: "Oh, you have to visit Time Square!" This is not my authority, everyone knows about Time Square.  

One of my tutors when I was training described my interest in must / have to as an obsession and so I may be taking this too far but I hope it helps.

Thanks

Jack Radford 

The LearnEnglish Team 

 

Hi Jack
my obsession with must and have to is as strong as yours (maybe even stronger). As far as school rules are concerned I wonder if it is better to use must or have to.
Students must wear uniforms comes from people in authority, but it is also a school rule (coming from somewhere else). Well, why can't I say Students have to wear uniforms then?
More examples: Students must do their homework / students have to do their homework.
Students must be punctual. / students have to be punctual.
Don't you agree?
Thanks for your most useful help (if any).
Ernesto from Italy

Hi Ernesto

This is an interesting example. Some of my teachers, the young friendly ones, would avoid using 'must' to deflect their students' negative reactions to being told what to do.

For example, if a young friendly teacher saw a student listening to an ipod (well, it would have been a walkman back then), they would tell the student to put the ipod away. However, they would appeal to the student saying:

"I understand you are upset. It's not my decision. It's a school rule, you have to put it away." 

Other teachers seemed to enjoy their roles as enforcers of the school's authority. They would be more likely to use must.

"You must listen to me!"

Thanks

Jack

The LearnEnglish Team

 

 

Thank you so much for your priceless help!

thanks , from such helpful descriptions about "Must and Have to" so, I hope you be fine all times .

ohh this is something really helpful :)

its useful to learn something of this topics...

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