Modal Verbs - How to Use Must, Have to and Should - English Grammar Lesson

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In this lesson, you can learn about the modal verbs must, have to and should.

Do you know the difference between 'must', 'have to' and 'should'?

English learners often mix up these three verbs.

In this lesson, you can learn how to use must, have to and should correctly in English.

Must and have to are both used to talk about obligations: things you cannot choose not

to do.

For example:

We must talk to her before she leaves.

I have to go into work early tomorrow.

If you say, We must talk to her before she leaves, you mean that you think this is very

important, and you need to do it.

When you say, I have to go into work early tomorrow, you mean that you have no choice.

These are both obligations, but they’re slightly different.

Can you see how they’re different?

The first obligation is more personal, which is why you use must.

You feel that it’s necessary and important to talk to her before she leaves.

The obligation comes from you and your feelings.

What about have to?

The second obligation is more situational, which is why you use have to.

It’s necessary to go into work early tomorrow, maybe because you have to meet a client, or

you have some important work to finish.

The obligation comes from the situation, not from you.

Let’s see some more examples:

I must pay him back like I promised.

--> You made a promise, and now it’s important to you personally to keep your promise and

pay him back.

He has to do a lot of homework every week.

--> He needs to do a lot of homework because the school gives him a lot of homework.

It’s rare to use must to talk about obligations in spoken English.

Native English speakers use have to much more in conversation.

However, you can use must to talk about obligations in formal or written English.

For example:

All passengers must have a valid ticket.

Candidates must arrive no later than five minutes before the scheduled start time.

Want an easy answer to this?

Here’s an easy answer: use have to when you speak.

Using must to talk about obligations can sound very formal and strange in spoken English.

If you use have to when you speak, you’ll never be wrong!

You can use must to talk about obligations in your written English if you’re writing

something more formal.

This doesn’t mean that you won’t hear must in conversation; actually, you’ll hear

it a lot.

Why is this?

Didn’t we just tell you not to use must in spoken English?

It’s because must has many other meanings, too.

Using must to talk about obligations is rare in spoken English, but you can use it for

many other things.

Okay, you’ve seen how must and have to are different.

What about mustn’t and don’t have to?

Wait, what?

We just talked about must and have to.

Isn’t this the same?

Not at all.

Must and have to aren’t exactly the same, but they are quite similar.

However, the negatives—mustn’t and don’t have to—are completely different.

Look at two sentences:

Visitors must not touch the paintings.

You don’t have to be here before ten.

Can you tell the difference?

Must not means that something is forbidden.

You are not allowed to do this.

If you’re in a museum, and the sign says Visitors must not touch the paintings, then

don’t touch the paintings!

Don’t have to means that something is not necessary.

You can choose to do something or not.

If we have plans, and I tell you, You don’t have to be here before ten, then you can be

here before ten if you want.

You can come at nine, at eight, or whenever you want.

It’s your choice.

Let’s see some more examples:

Passengers must not talk to the driver while the bus is moving.

--> It’s forbidden to talk to the driver while the bus is moving; you aren’t allowed

to do this.

You don’t have to finish it today.

--> You can finish it today if you want to, but you can also leave it until later if you

want.

It’s your choice.

Like must, must not is more common in formal or written English.

In spoken English, it’s more common to use can’t.

For example, you might see a sign saying:

Mobile phones must not be used while driving.

But, if you were talking, you’d probably say:

You can’t use your phone while you’re driving.

On the other hand, don’t have to is common in both spoken and written English.

So now you’ve seen the difference between must and have to, but what about should?

Remember that must and have to can be used to talk about obligations.

Should is different.

You use should to give advice or express your opinion.

For example:

You should go to bed earlier.

Then you wouldn’t feel so tired all the time.

--> This is my advice.

I think it’s better for you to do this, but it isn’t necessary.

It’s not an obligation, so you still have a choice.

He should do more work if he wants to get promoted.

--> This is my opinion.

I don’t think he needs to do it, and I don’t necessarily care if he does this or not.

You can’t use should to talk about obligations or rules.

When you say,

You should…

You mean that the person has a choice.

You’re giving your opinion or some advice.

However, must can also be used to give advice.

For example:

You must try the fish.

It’s delicious!

Actually, you can also use have to to give advice.

You could also say:

You have to try the fish.

It’s delicious!

Can you tell the difference between using should to give advice, and using must or have

to?

Giving advice with must or have to is stronger and more emphatic than giving advice with

should.

If you say:

You should try the fish.

This sounds quite neutral, but if you say:

You must try the fish!

Or, You have to try the fish!

These sound much stronger.

You’re more excited about what you’re saying.

You really like that fish!

So, you can use must, have to or should to give advice or express opinions.

Using must or have to expresses stronger feelings than just using should.

However, if you want to give negative advice, only shouldn’t is possible.

For example:

You shouldn’t eat so much chocolate at once—you’ll make yourself sick!

You shouldn’t take the job unless you’re sure it’s what you want.

In negative sentences, you can only use shouldn’t to give advice or express your opinion.

You can’t use mustn’t or don’t have to with this meaning.

At this point, you’ve seen how to use must, have to and should to talk about obligations

or advice.

Let’s put everything together by comparing all three verbs.

Use must for:

Obligations you feel strongly about: I must remember to send him a birthday card.

Obligations in formal, written English: All employees must wash hands.

Strong advice: You must read it—it’s an amazing story!

Saying something is forbidden, if you use mustn’t: Children must not be left unattended.

Remember that mustn’t or must not are more formal, and in spoken English it’s more

common to say can’t.

Next, what about have to?

You use have to for:

Obligations which depend on rules or circumstances: I have to wear glasses because I can’t see

so clearly.

Most obligations in spoken English: Do you have to work tomorrow?

Saying something is not necessary: You don’t have to do this if you don’t want to.

Strong advice: You have to try this ice cream!

Using have to for strong advice sounds more conversational than using must.

Finally, should.

You can use should for:

Giving advice: You should try once more—I’m sure you can get it.

Giving negative advice: You shouldn’t work so hard.

Take a break sometimes!

Giving your opinion: If they make us work overtime, they should pay us for it.

One last point: these three verbs can also be used to talk about probability and certainty.

In this video, we focused on talking about obligations and giving advice, but these verbs

can also be used in other ways.

So now you’ve seen how to use must, have to and should in different ways.

Want more practice with this topic?

Check out the full lesson on our website: Oxford Online English.com.

You can read the script and practice with a quiz.

Thanks for watching!

See you next time!