Modal verbs are used to express functions like obligation, permission, advice, possibility and necessity. Common modal verbs include can, could, shall, should, may, might, must, ought to. They are used with other verbs to express things like obligation (must, have to), permission (can, may), advice (should, ought to), deduction (must, can't) and past possibility (could, might). The document provides examples of using different modal verbs in sentences to convey obligation, permission, advice and other meanings.

1. MODAL VERBS

2. What are modal verbs?
• Modal verbs (also called modal verbs, modal auxiliary verbs,
modal auxiliaries) are special verbs that give additional
information about the function of the main verb.
• Examples : CAN, COULD, SHALL, SHOULD and so on.
• Types of modal verbs
1.Advice
2.Obligation
3.Permission

3. Modals
• Modals in the present
: You should see a doctor.
• Modals in the past
: You should have seen a doctor

4. Advice
Modal Verbs OF

5. - Use to give advice and make recommendations.
- For example:
- I think you shouldn’t lazy to do your homework.
- We should wake up in early morning because we must go to school.
• Should is used for advice in the present.
• Should is used for advice in the past.
• For negative advice.
Should

6. Ought to
- Similar to should but less common speech and
usually not used in negative way
- For example:
- You ought not to steal your mother’s money.
- You ought to study hard for the bright future.
• For negative advice

7. Had better
- Stronger and more urgent than should or ought to, so it
used to give
stronger advice and warning
- For example:
- It looks like rain, you had better take an umbrella.
- She had better hurry up because the train leaves in 5
minutes.
• For negative advice

8. Obligation
Modal Verbs OF

9. Obligation
• OBLIGATION means something by which a person is obliged to do,
and which arises out of a sense of duty or results from custom, law,
and so on.
• We can use
• - have to + infinitive (V.1)
• - must + infinitive (V.1)
• - should + infinitive (V.1)
• to express obligation (Something you have to do)

10. Have to /
Don't have to
Positive Obligation Negative Obligation
☀ Use for strong obligation
☀ This is usually referring to a rule or law
Examples:
-Children have to go to school.
-You have to be careful with scissors.
☀ Use "Don't have to" to show
something that is not necessary
Examples:
-I don't have to work on Sundays.
-You don't have to eat anything you
don't like.

11. Had to /
Didn't have to
Positive Obligation Negative Obligation
☀ Obligation in the past
Example:
-I had to wear a school uniform when I
was a child.
☀ No obligation in the past
Example:
-We didn't have to go to school on
Saturdays.

12. Must (Must Have) /
Mustn't
Positive Obligation Negative Obligation
☀ Strong obligation (possibly based on
the speaker's opinion)
: I must study today.
☀ It is formal and normally used in
writing
:You must use a pencil on the test.
☀ Logic/Certainty or strong probability.
: She must be hungry because she has
not eaten for 2 days.
☀ MUST HAVE: use in supposition
: I can't find my laptop, I must have left
it in the train.
☀ "Must not" shows something that
is prohibited
Examples:
-You mustn't smoke here.
-You mustn’t eat in the computer room.
(Food in the
computer room is prohibited.)

13. SPECIAL EXAMPLE
• Take care to distinguish correctly between "had to" and "must
have"
• They had to go to Thailand.
= They were obliged to go to Thailand.
Vs.
• They must have gone to Thailand.
= In my opinion, they have certainly gone to Thailand.

14. Should have + past participle /
Shouldn't have + past participle
Positive Obligation Negative Obligation
☀ A past action which didn't happen.
Example:
-You should have gone to bed earlier,
now you have missed the train.
☀ A past action which didn't happen.
Example:
-You shouldn't have taken that job, it
was a bad idea.

15. SPECIAL EXAMPLE
• Here is an example of the difference between 'have to' and 'must':
• -My doctor said that I have to stop smoking or I'll risk serious
problems. (I have no choice)
Vs.
• -I must stop smoking. It’s costing me too much money. (It’s my
decision)

16. NOTE TO SELF:
• Be careful about the difference between don't have to and
mustn't!
• Don't have to means you don't need to do something, but it's
fine if you want to do it:
• -I don't have to get up early at the weekend (of course, if I want
to get up early, that's fine, but I can stay in bed if I want).
• Mustn't means it's not allowed, or it's a bad idea:
• -You mustn't eat so much chocolate, you'll be sick.

17. Should (Ought to) /
Shouldn't
Positive Obligation Negative Obligation
Mild obligation
Advice
Logic/Conclusion
Examples:
-You should save some money.
-I ought to get a haircut
Mild negative obligation
Advice
Examples:
-You shouldn't smoke so much.
Should and ought to are more or less synonymous
Example:
-You should stop smoking. = You ought to stop smoking.

18. Permission
Modal Verbs OF

19. Definition of PERMISSION
: the right or ability to do something that is given by someone
who has the power to decide if it will be allowed or
permitted

20. Ask For Permission
• We often use “can” to ask for permission.
Ex. Can I go home now?
Can we eat this pizza?
• Could is more formal and polite than can.
Ex. Could I play a video games?
Could I smoke at the school?
• May is another more formal and polite way.
Ex. May I go to shopping?
May I drink water?

21. Give Permission
• We also often use “can” to give permission
Ex. You can go home now.
You can eat this pizza.
• Could is more formal and polite than can, and we use could to say that
something was permitted in the past
Ex. You could play a video games .
You could smoke at the school 15 years ago.
• May is more formal and polite way to give permission
Ex. You may go shopping.
You may drink water.

22. Refusing Permission
• We use “can’t” to say that something isn’t permitted.
Ex. You can’t go how now.
You can’t eat this pizza.
• We use “couldn’t” to say that something was not permitted in the past.
Ex. You couldn’t smoke in the bus.
You couldn’t do exercise in the toilet.
• We can also use “may” to say that something isn’t permitted too.
Ex. No, you may not.

23. TEST YOURSELF
• You don’t look very well, you __________ go to
work.
had better not

24. TEST YOURSELF
• Mrs. Johnnie's body was found in
the lounge just moments ago, and
it's still warm! Nobody has left the
mansion this evening, so the killer
______ be someone in this room.
It ______ be any one of us!!!
must
could

25. TEST YOURSELF
• She __________ get up early today, because it's
Sunday.
doesn’t have to

26. TEST YOURSELF
• You ______ tell anyone what I just told you. It's a
secret.
mustn’t

27. TEST YOURSELF
• Ned: ______ I borrow your lighter for a minute?
Sarah: Sure, no problem. Actually, you ______ keep it
if you want to. I've given up smoking.
Can
can

28. Thank you for listening.
Jitrapa Leetanasaksakul No.3
Tanasorn Pajchim No.7
Apichaya Wanwaisart No.11