Modal verbs have special characteristics such as not changing form for third person singular, requiring the base verb form, and some taking a preposition. They are used to express ideas like ability, permission, obligation, advice, speculation and suggestions. While most modals don't have past tense forms, perfect modal constructions can be used with "have" to talk about past ability, obligation or speculation. Different modals have specific meanings like "must" and "have to" for obligation and "should" and "ought to" for advice.

1. Modal verbs

2. Modal verbs have special characteristics
1)They are auxiliaries. You don’t use auxiliary verbs with them. You say:
I shouldn’t eat a lot of hamburgers.
NOT I don’t should eat a lot of hamburgers
You say:
Can I go to the toilet?
NOT Do I can go to the toilet?

3. More special characteristics
2) They don’t change with the 3rd person singular.
I must wake up early → She must wake up early
I may go to your party → He may go to your party
I could jump very high → It can jump very high

4. More special characteristics
3) They are followed by the INFINITIVE (base form).
You say:
Kevin must study for his exam.
NOT
Kevin must studies for his exam.

5. More special characteristics
4) They don’t have gerunds or participles.
You DON’T SAY:
Kevin is musting study today
Kevin has musted study today.

6. Not all modals are the same
● Most modals don’t use the preposition to:
You should study
She must drive her father’s car
I would like to go to that concert

7. Not all modals are the same
BUT some modals need the preposition to:
You ought to study
She has to study
I used to live in Korea

8. Not all modals are the same
Two modal verbs are actually semi-modals. They change in
the third person singular. They are HAVE TO and NEED TO.
Laura has to work on Sunday
Paul needs to clean the kitchen
Jean doesn’t have to go to the office

9. Not all modals are the same
They also have a past form.
Laura had to work on Sunday
Paul needed to clean the kitchen
Jean didn’t have to go to the office
Most of the other modals don’t.

10. obligation modals

11. must and have to
We use must and have to to express obligation.
You must bring a bottle of water to the gym.
You have to wear sport shoes to the gym.

12. must and have to
They change meaning when they are negative:
You mustn’t bring food to the gym. (It’s forbidden)
You don’t have to bring your MP3. (You can if you want to)

13. must and have to
It’s not very common to make questions with must.
Must I go every day? → 😶❔
We usually make questions with have to.
Do I have to bring a towel?→ 😊 ✓

14. need/ needn’t
You can also use need to to express necessity or obligation.
I need to take these documents to my boss.
In the negative, needn’t means lack of obligation.
You needn’t bring your MP3 to the gym.

15. modals for advice

16. should / ought to
We use should and ought to to give advice.
You should eat more fruit
You ought to visit your grandmother
You shouldn’t drive so fast
Should I buy that shirt?
It’s not very common to use ought to in the negative (oughtn’t) and interrogative
forms.

17. modals for ability

18. can / could / be able to
We use can to express our ability to do something.
Beyonce can sing very well.
Louis can’t play the piano.
Can you run 12 kilometres?

19. can / could / be able to
Unlike many modals, can has a past form, could.
Pavarotti could sing very well.
Napoleon couldn’t conquer Russia.
Could you arrive to the theatre on time yesterday?

20. can / could / be able to
For the future and other times, we use be able to:
I will be able to see Kim in London this summer.
I won’t be able to go to your party.
He’s been able to finish his homework in 6 minutes.
Jane hadn’t been able to talk to her mum in Australia.

21. permission
We can also use can / could to ask for permission. Could is
more polite. You can also use may.
Can I go to the toilet? No, you can’t.
Could I use your phone? No, I’m sorry.
May I come in? No, you may not.

22. suggestions and offerings
You can make suggestions and offerings with can. Could is more polite.
You can use my computer if you want to.
You could try the subway next time.
You can also use shall. This is old-fashioned and polite.
Shall we dance?
You can also use would to make polite offerings
Would you like to dance?

23. modals for speculation

24. We are not very sure
When we are not sure of something, we can use could, may,
might.
It may be Karen’s boyfriend.
It could be Karen’s boyfriend.
It might be Karen’s boyfriend.

25. We’re positive
We usually use must.
It must be Karen’s boyfriend. She’s kissing him.

26. When something is impossible
We usually use can’t.
It can’t be Karen’s boyfriend. He lives in France.

27. can’t / cannot /couldn’t
You can use can’t and cannot to forbid something.
You can’t smoke in school.
BUT you musn’t use couldn’t to make it more polite. It means
you weren’t able to do something in the past.
You couldn’t smoke in school in 1979.

28. Modals in the past :
modal perfect verbs

29. how to use them
Because we usually can’t use the past tense with modals, you
add have in the infinitive form and a participle. That is, you say
things like:
I must have forgotten my wallet.
He may have missed the bus.

30. modal perfects for speculation:
not sure
I saw Karen with someone yesterday.
It may have been her boyfriend.
It might have been her boyfriend.
It could have been her boyfriend.

31. we’re sure
They were kissing.
It must have been her boyfriend.

32. it’s impossible
It can’t have been her boyfriend. He wasn’t in Madrid.

33. For extra
practice:
For more information and exercises,
you can also visit:
BBC Learning English
Learn English Teens -British Councilhttp://www.agendaweb.org/verb
s/modals-exercises.html