Have to and must

Have to and must

Obligation

Have to and must are both used to express obligation. There is a slight difference between the way they are used.

We use "have to"

• To talk about obligations and rules.

It shows us that the obligation comes from somebody else (from “outside”). It’s a law or a rule and the speaker can’t change it.

Examples:

Do you have to wear a uniform at your school?

John can’t come because he has to work tomorrow.

In Britain you have to buy a TV licence every year.

We use "must"

• For giving strong advice to ourselves. I must try to get to bed early tonight.

• For making strong recommendations to others, based on our own opinions. You must try this cake, it´s wonderful.

• For stating rules, especially in written and formal English. Cyclist must wear helmets.

It shows us that the obligation comes from the speaker. More examples: I must call my dad tonight. You must hand in your homework on Tuesday or your mark will be zero. You must come and visit us the next time you come to London.

Must and have to are very similar, but there is a small difference. We normally use have to for a general obligation (a rule at work or a law). We normally use must when the speaker imposes the obligation (for example, a teacher to students or a parent to children). But often you can use either.

No obligation

We use "don’t have to"

• For things we do not need to do. It expresses a lack of obligation, it does not express prohibition.

• Examples:

You don´t have to leave now. You can stay as long as you like.

You don’t have to wear a tie in our office. You can wear a tie if you want to but it’s OK if you don’t.

It’ll be nice if you do but you don’t have to come with me if you don’t want to.

You don’t have to dress up for the party. Wear whatever you feel comfortable in.

Prohibition

We use "mustn´t"

• For prohibitions.

• You can use mustn´t or can´t to talk about rules.

• Examples:You mustn´t smoke here. We mustn´t talk about it. It is confidential.

Mustn´t and don´t have to have completely different meanings.

Compare: You mustn´t go = You can´t go. It´s prohibited.

You don´t have to go = You can go if you want, but it´s not obligatory/necessary.

Exercises:

Complete the sentences with the appropriate word.

have to, don´t have to, mustn´t , must

1  You __________ memorize it - but try to remember the key points.

2 You __________ hit your sister again! Do you understand?

3 You __________ phone me at work. We aren´t allowed personal calls.

4 You __________ come to the meeting but it would help us all if you´re here.

5 I __________ stay on for a few hours because I´d rather work late today than over the weekend.

Choose the correct verb for these sentences:

1 You can/ have to start saving money if you want to retire early.

2 You don´t have to/ must try this cake, it´s delicious.

3 I don´t have to/ mustn´t eat chocolate. It´s bad for me.

4 You must/ mustn´t be late for class.

5 You must/ mustn´t listen when the teacher talks.

Sources:

http://learnenglish.britishcouncil.org/en/quick-grammar/modals-1

http://www.ecenglish.com/learnenglish/lessons/modal-verbs-1-permission-prohibition-obligation-no-obligation

https://www.englishgrammarsecrets.com/musthaveto/menu.php

https://www.englishgrammarsecrets.com/musthaveto/menu.phpsometime

http://www.englishservice.cz/download/Must%20have%20to.pdf

Davies, Paul A and Falla, Tim. FCE Resutl Student´s book. Oxford: Oxford University press, 2008.

Oxenden, Clive, Latham-Koenig, Christina and Seligson Paul. New English File Pre-intermediate Student´s Book. Oxford: Oxford University press, 2007.

Oxenden, Clive, Latham-Koenig, Christina and Seligson Paul. New English File Pre-intermediate Teacher´s Book. Oxford: Oxford University press, 2007.