decided that something is necessary.
Must expresses an obligation from the speaker’s point of view, an obligation imposed by the speaker; it is used to give a strong personal opinion: The dogs believe they must keep it a secret.
As must expresses a strong obligation, we do not often use it in face-to-face conversation as it can sound impolite and often inappropriate. We often use should and ought to as an alternative to must as they express a subjective (often moral) obligation felt by the speaker, but the obligation is weaker than with must
You should treat your neighbours with more respect and never bark at their cats.
2. Prohibition; refusing permission
Must is used in negative sentences when it is forbidden/prohibited to do something; you are not allowed to do something; it is against the rules/laws:
The dogs were astonished when they saw: «You mustn’t go by train if you haven’t got a ticket (even if you are a dog).»
3. Command, urgent request, command in public notices or documents:
You must do as you are told.
In the present we can use both forms: must and have to.
Remember the difference in sentence formations: we use auxiliary do/does for to have to while making questions and negative sentences: Do the dogs have to buy train tickets? – No, they don’t have to do it.
Must is similar to have to but we use have to (not usually must) to say what someone is obliged to do: Luna has to let her parents know where she is. (She is obliged to do it, it’s not her intention)
Mustn’t and don’t have to are completely different:
You mustn’t do something = it is necessary that you do not do it (so don’t do it):
You don’t have to do something = you don’t need to do it (but you can if you want):
EXERCISE 1
Complete the sentences with must/mustn’t or have to/has to/don’t/doesn’t have to.
1 The dogs ***** get into the train again to find Kit.
2 They ***** worry. Kit is clever enough to find the way back home.
3 Anyway, the kitten ***** be left alone on the train.
4 Does everybody ***** return or does Luna alone ***** look for the pet?
5 The dogs have decided they ***** do everything together.
6 Whatever they do, they ***** separate.
7 They got into the train again and suddenly saw the poster: «If you have lost each other on the train, you ***** panic. Use our radio to make an announcement.»
TO HAVE TO
When we talk about past obligations or necessity, we use had to. The dogs had to come back.
Future obligation can be expressed by must or made more precise with will have to.
They will have to get back to the forest as soon as they find the kitten.
The form have to is also used for Perfect Tenses.
They have just had to get into the train again.
They had had to do it very quickly before the train left.
They will have had to return to the forest before dark.
Must has no infinitive, gerund or participle forms. So when necessary, we make this form with have to.
Chilly hates having to waste time.
He never used to have to take care of pets.
Having to look for Kit, the dogs might waste a lot of time.
EXERCISE 2
Complete the questions with the correct form of have to/must and answer them:
1 Is there anything you ***** do for your job or study which you hate?
2 When was the last time you ***** catch a train?
3 Name two things you ***** do every day.
4 What do you hate ***** do?
5 What did you use to ***** do when you were little?
6 What would you ***** do if you were shipwrecked?
7 What will you ***** do to save money for a rainy day?
EXERCISE 3
Complete the sentences using the proper verb and the correct form of must/have to: tell, bark, come back, run, get away, face, pinch, look for
1 The dogs ***** along all the aisles looking for the kitten but couldn’t find him anywhere.
2 Luna was extremely furious because of ***** Kit a dozen times that he ***** from her.
3 ***** the kitten in every corner of this long train, the friends were getting angrier and angrier, more and more exhausted.
4 They had already lost any hope to find the kitten on the train and thought of ***** to that platform when Chilly made a sudden stand.
5 He couldn’t believe his eyes and ***** himself to make sure it was not a hallucination.
6 There was somebody’s sweater on a berth and Kit enjoying such a balmy sleep on it that Chilly ***** loudly to wake him up.
7 When Kit realised what had happened, he got so embarrassed that was ready to do anything to avoid ***** Luna.
SHOULD AND OUGHT TO
