Oliver and Alfie visit the local pet shop, where they are surprised to see Amy. Meanwhile, something is on Sophie's mind ... 

21

We use have to / must / should + infinitive to talk about obligation, things that are necessary to do, or to give advice about things that are a good idea to do.

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

I 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.

I 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 seat-belts.

Do they change in form for I, you, he, 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.

I think I’ve heard have got to. Is that correct?

Yes, we use both have got to, for obligation, and had better, for advice, a lot in speaking.
 
You've got to be careful with a cat
You'd better get something a bit quieter.
I'd better go – I mustn't miss the helicopter! 
              

So they’re not used in formal writing?

No. 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)

Umm, I’m still a bit confused ...

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.

Ah! Right, I mustn’t forget that.

No, you mustn’t! OK, let’s look at advice, telling people what you think is a good idea. We use should for advice, or making suggestions, and must for strong advice.

You must go for a walk with the dog at least once a day.
Maybe you should go for a coffee or lunch and see how you feel?
You shouldn't leave it on the street.

I think I’ve heard people use should in other ways, like 'he should be here in a minute' – that’s not advice, is it?

No, that’s talking about what is likely or probable. We’ll look at that use another day. We use modal verbs in different ways.

I see. So I should think about one use at a time.

Yes, exactly. You mustn’t get confused by too many uses at once.

 

Total votes: 809
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Discussion

Have you got a pet? If you haven't got one, what kind of pet would you like? What are the advantages and disadvantages of having that particular animal? 

Comments

Jo - Coordinator's picture
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Jo - Coordinator 13 July, 2017 - 14:27

Hi ph16c033! It's grammatically possible to say that but it depends what you mean. What do you want to say? If you're just saying it's an obligation to go to Mumbai, it's not necessary (and it's actually incorrect) to use 'must' and 'have to' at the same time. Best wishes, Joanna (LearnEnglish Teens team)

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janie's picture
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janie 23 March, 2017 - 02:08

When I was a child, I watched the film:"Kommisar Rex". I always dream that one day I have one dog like this. Eventually, my dream has come true. I have a German Shepherd Dog. He is very big and smart. If any thieves intend to break into my house, it will be the biggest mistake in their life. The disadvantage is that I have to clean him every week and spray insecticide every month for prevention of fleas and ticks.

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46 users have voted.
Elu17's picture
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Elu17 28 February, 2017 - 19:27

One of the pets I have at home is a budgie. She is such a playful bird but a huge distraction while I am studying.

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40 users have voted.
Mabdelaziz's picture
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Mabdelaziz 3 December, 2016 - 17:01

Hi learn English team ,
hop you all doing well.
I have a question please it about the above practice.
Why I have to say 1-"Why do we always have to come to the same cafe?
And I mustn't say 2- "Why we always have to come to the cafe?
What is the different between two sentence?

Thank you so much for you usual support.

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67 users have voted.
Jonathan - Coordinator's picture
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Jonathan - Coor... 4 December, 2016 - 14:30

It’s a question, and most questions need to have an auxiliary verb (unless they are with a modal verb like “can” or “should”).
In this example, the verb is “have to”, which needs some form of “do” as the auxiliary verb (“do” or “does” in the present simple, “did” in the past simple). So --> “do we have to”. 
Jonathan (LearnEnglish Teens Team)

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74 users have voted.
EriD's picture
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EriD 8 November, 2016 - 23:04

I had got a pet. It was cat and reptiles. I like snake and lizard and gecko. Of course I like cat and dog too.

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63 users have voted.
AloBenveB's picture
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AloBenveB 2 September, 2016 - 02:42

I had a Sirio Hamster, its name was Natasha Romanov, she was very cute, nice and above all a good companion and great friend. I had to clean each week the substrate of her cage. I think that a hamster as pet is a good idea, however, you should buy toys and have to play with it.
Moreover, you must provide a correct diet, this must not contain high fats levels and acid fruits as a lemon.
Now, I am considering If I should buy a Chinchilla, I love this kind of pet, however, I should not buy it because my mom dislikes animals.

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80 users have voted.
hgsmf's picture
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hgsmf 21 August, 2016 - 03:44

No, I do not have a pet, but I want to buy a cat.Its advantages that it will give me love and it will be my friend and play with me .Its disadvantage that my sister my be afraid from it because she is so little to adapt with a cat in the home .

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76 users have voted.
NI12's picture
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NI12 2 November, 2015 - 16:38

I haven't got any pets, but I would like to have a dog. A disadvantage is that you must go for a walk with the dog at least once a day, but when you love your dog you will see that there are also many advantages. You can learn a lot from it and it will give you a lot of satisfaction.

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118 users have voted.
donya123's picture
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donya123 19 October, 2015 - 19:10

I had once a rabbit. She was quite sweet and lovely.The thing I did not like at him was her smell. I had to clean every two days her cage and she always scratch me, when I hold her.

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118 users have voted.
nawaki's picture
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nawaki 22 August, 2015 - 13:32

I don't have a pet.I like cats and hamsters.
The advantage of having that particular animal are:learning a lot of things about animals like how do they live and learning about the animal world ,but the disadvantage is that you must be responsable completely for his life.

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134 users have voted.