As you watch the video, look at the examples of have to, must and should. They are in red in the subtitles. Then read the conversation below to learn more. Finally, do the grammar exercises to check you understand, and can use, have to, must and should correctly.
Oliver: Amy! Hi! What are you doing here?
Amy: It's my new Saturday job. Hi, Alfie.
Amy: Yes. I want to study veterinary science at university and my parents suggested I should get some experience of working with animals.
Oliver: And do you like it?
Amy: It's my first day ... Anyway. What can I do for you?
Oliver: Well, I've got some money and I've decided I'd quite like a pet. Daisy and Mum like the idea, but Mum says I mustn't get a spider, a scorpion or a snake.
Amy: That's understandable.
Alfie: Let's see the dogs. Oh yeah! Look at these, mate! Puppies! What's that white one?
Amy: That's a Dalmatian.
Alfie: But they've got black spots, haven't they?
Amy: Not when they're puppies, no. You have to wait until they're bigger. Then the spots appear.
Alfie: Ah, I never knew that. Dalmatians are quite big, aren't they?
Amy: Yes, they are. You should really have a garden.
Oliver: Well, we've got one ...
Amy: And you have to take them out for a walk twice a day. Well, you don't have to go twice, but you must go at least once. Every day. Rain, snow, sun ... every day. And you mustn't forget to take two or three small plastic bags when you go out.
Oliver: Plastic bags?
Amy: Well, when your dog … you shouldn't leave it on the street. You should always clean it up and put it in the bin.
Oliver: Hmm. And a smaller dog? Should I get one of these?
Amy: They're Yorkshire terriers. They're very small ...
Alfie: ... and noisy! You'd better get something a bit quieter, Ollie. Think of your neighbours!
Oliver: How about that one?
Amy: As an adult, Old English Sheepdogs are extremely large – like that one. And you've got to look after their hair regularly. You should brush them as often as possible, and get their hair cut.
Oliver: Hmm. What about a cat?
Alfie: We used to have a cat. She was a bit unfriendly. She used to scratch the sofa – and our legs – and she stole food if you left it for a moment. You've got to be careful with a cat – some are nice, but some are ... well ...
Oliver: Oh, ff. A turtle? They're small and quiet and they don't have hair ...
Amy: They grow. And then you have to buy a bigger tank. You'd better buy a thermostat and a filter if you want a turtle. And you mustn't forget to change the water; they don't smell great ...
Oliver: What about a hamster?...
Sophie: I don't know what I should do. I mean, I don't want you to feel uncomfortable ...
Daisy: I don't mind! And if you like him ... why not? He has to decide if he wants to go out with the mother of a student, though. But he seems nice. Maybe you should go for a coffee or lunch and see how you feel? If you don't like him, you don't have to see him again.
Sophie: I shouldn't be asking you about this sort of thing! Oh, but I feel like a teenager. Why do these things have to be so complicated?
Daisy: It's not complicated, Mum! You mustn't forget, he's the one who suggested going for a drink, so he obviously likes you – and you obviously like him! What's complicated?
Sophie: I'm in New Zealand! I'm about to go and fly over volcanoes ... it's not easy to combine my kind of life with ... well, with a romance!!
Daisy: You'll be home next week, and maybe you should take some time off travelling. Spend some time with us. And with him. And I'll be leaving school in a year ... so ... go on, Mum. Life's too short! You should phone him!
Sophie: Well, I'll think about it. I'd better go – I mustn't miss the helicopter! Is Oliver there?
Daisy: No, he's out buying that pet ... ah no, here he is. Ollie, it's Mum.
Oliver: Hi, Mum!
Sophie: Did you get anything?
Oliver: Yes I did! And his name's Hannibal.
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.
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?