Английская грамматика: модальные глаголы

9. Instructions and requests:
We use could you as a polite way of telling or asking someone to do something:
Could you take a message please?
Can is less polite:
Can you take a message please?
10. Offers and invitations:
We use can I … to make offers:
Can I help you?
2. Modal verb. Must
Теория:
Study the information about ‘must’ .
Must
1. To express obligation or duty.
This also refers to laws and regulations.
You must wear a seatbelt at all times.


2. To emphasize the necessity of something.
You must study hard before the test.
You must drive carefully.
3. Deduction - sure that something is true (Certainty).
We use this when we don't know but we are certain that it is true (based on evidence).
Dinosaurs were huge, they must have eaten a lot.

4. Expresses positive logical assumptions (Must + have + past participle).

He must have won the lottery with the new house and car he has just bought.

5. A strong recommendation.
Something that is highly recommended (stronger than using should)
The ice cream is delicious. You must try some.


Mustn't
The negative is mustn't which refers to prohibition (negative obligation)
Mustn't = Must not
You mustn't use your mobile phone while you are driving.

3. Modal verbs. Must and have to
Теория:
Study the differences between must and have to.
1. Must can be replaced by have to with little difference in meaning:
You have to study. (= you must study)

2. Have to is a more informal while Must is mostly used in written orders or instructions.
Boss: You must complete this work by Friday
Worker: We have to complete this essay by Friday.