Must vs Have to

You see many rules at school, at home, and of course, in public places. However, you may see or hear different structures when people set rules. Now, let’s take a look at these two different structures of obligation.

We use have to / must / should + infinitive to talk about obligation, things that are necessary to do.

Must and have to are both used for obligation and are often quite similar. They are both followed by the infinitive.

must go now. / I have to go now.

Are these exactly the same?

Well, almost. We often use must for more personal opinions about what it is necessary to do, and have to for what somebody in authority has said it is necessary to do.

must remember to get a present for Daisy.    (my opinion)   
You have to look after their hair regularly.     (dog experts say so)
Do you have to wear a tie for school?    (asking about school rules)

Which verb do people use more?

Have to is more frequent in conversation; must is used more in formal writing, for example in written notices.

Passengers must fasten their seatbelts.

Do they change in form for I, youhe, she, etc.?

Have changes in the third person singular (he/she/it has); but must doesn’t change. It’s a modal verb and modals don’t change.

There’s something very important about must and have to.

The positive forms are very similar in meaning, but the negative forms are completely different.

You mustn’t forget …
(don’t forget – you have no choice)
If you don’t like him, you don’t have to see him again.
(there is no obligation to see him again, but you have a choice)

Here’s an example you can remember:
In a non-smoking area, you mustn’t smoke, but in a smoking area you don’t have to smoke but you can if you want to.

You mustn’t forget what we have discussed above. Now it’s your turn to set the rules. You can start setting the rules in your room or your house.

Source: “Have to, must and should for obligation and advice” Learn English Teens British Council, British Council The United Kingdom,

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