How to Use Must, Should, and Have To Correctly

Using must, should, and have to can be tricky for English learners. Even though these modal verbs express similar meaning, they have different usage, and using the wrong one can lead to misunderstanding in some situations.

To help you understand these modal verbs better and use them correctly so you can avoid possible misunderstandings and sounding awkward, here’s a short description of each of them.

How to Use Must

Use this modal verb to give orders, express obligation, or give advice. You can only use it for present and future situations. If you want to refer to the past, use “have to” instead of must.

You can use must in the following situations:

• When you want to give orders in a firm and positive manner.

Ex. You must eat now.

• When you want to express obligation.

Ex. All of you must hand in your project before 1st of May.

• When you want to give advice or recommend something to someone:

Ex. You must visit Paris - it’s wonderful.

• When you want to say that you’re sure something is true.

Ex. She must be joking.

Ex. He looks a lot like John. He must be his brother.

How to Form Negative Sentences with Must

To form negative sentences with this modal verb you need to add “not” after must – must not, or mustn’t. You use it in negative sentences when you want to forbid something or when you want to say that some state or event is unacceptable. The formula to follow is:

Subject + must not/mustn’t + verb + object

Ex. You mustn’t tell her that I did that.

Ex. There’s mustn’t be any grammar mistakes in your English exam.

How to Form Questions with Must

To form questions with must, start with the modal verb followed by the subject. If the formula for positive sentences with must is Subject + must + verb + object, the formula for questions with this modal verb is:

Must + subject + verb + object

Ex. She must take the medicine. – positive sentence

Must she take the medicine? – question

How to Use Have To

“Have to” is another modal verb although it doesn’t look like one. It’s the modal verb with the most similar meaning to must, so they are often used interchangeably. But, there’s still a difference between them.

Both modal verbs express necessity and obligation, but must is used when the speaker sets the rule, while have to when someone else is setting the rule. The speaker neither sets nor can change the rule. It’s a general rule you can do nothing about it like going to work.

Another difference is the emotional context. While must expresses the feelings of the speaker, have to expresses a general, impersonal idea. You can use “have to” to refer to the present, past, and future.

Use “have to” in the following situations:

When you want to say that something is obligatory:

Ex. People have to go to work.

Ex. I have to pay my energy bills today.

When you want to say that you’re following your moral principles, conscience, or duties:

Ex. I have to be honest with you.

How to Form Negative Sentences with Have To

When used in the negative form, this modal verb implies that something is not obligatory but the person can still do it if they want to. To form negative sentences you need to use don’t/doesn’t before the modal verb.

The sentence structure would follow the following formula:

Subject + don’t/doesn’t + have to + verb + object.

Ex. I don’t have to work during the weekends.

How to Form Questions with Have To

To form questions with “have to”, you need to start with the auxiliary do/does. Here’s the formula to follow:

Do/does + subject + have to + verb + object

Ex. Do you have to go to work tomorrow?

Ex. Does she have to see the doctor?

How to Use Should

Should is a modal verb with several uses, the most common one being making recommendations and giving advice. It can also express obligation, but much weaker than must and have to.

It functions as an auxiliary verb that comes before the main verb in a sentence. It’s never followed by “to” or by another modal verb.

Use “should” in the following situations:

• When you want to make a recommendation, offer your opinion, or give advice.

Ex. You should visit a doctor.

Ex. You should learn more if you want good grades.

Ex. They should ban smoking in public places.

When you want to indicate some duty, obligation, or correctness when criticizing someone.

Ex. I should be home at 11PM.

Ex. You should always look left and right before crossing a street.  

Ex. You should drive slower.

• When you want to express probability:

Ex. The bus should be here soon.

Ex. They should have finished studying by now.

• How to Form Negative Sentences with Should

To form negative sentences with should, just add “not” after it – should not/shouldn’t. The shorter form is more common, but the longer one is more appropriate in formal contexts to emphasize a key point. There’s no don’t, doesn’t, or didn’t with this modal verb.

Subject + should not/ shouldn’t + verb + object

Ex. You shouldn’t go the party because you’ve got a lot to study.

Ex. We should not forget the people who saved us.

How to Form Questions with Should

To make questions with should, just switch the positions of the subject and the modal verb.

Should + subject + verb + object

Ex. Should I come tomorrow?

Ex. Should we invite Mark and Ross to the party?

Question Tags with Should/Shouldn’t

Should and shouldn’t are also used in question tags when you want to ask for confirmation. When used in this way, this modal verb means “Do you agree?” or “ Is that right?”.

To form a tag question with should or shouldn’t, add it at the end of the sentence. If the sentence is a positive statement, you add shouldn’t, if it’s a negative statement, you use should.

Ex. She should have told Mary, shouldn’t she?

Ex. I shouldn’t wear something else, should I?

Conclusion

Must, have to, and should can cause confusion to English learners as they are all modal verbs with similar meaning. But, understanding their differences is not as difficult as you may think. Once you learn the most common uses of these modal verbs and how they form sentences and questions, you’ll be able to use them easily and correctly.