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
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Apichaya Wanwaisart No.11