1. Modal Verbs
Should vs. Have to

2. Modal verbs of obligation:
Have to (and must):
We can use have to, must express obligation. This means there is no other choice, or bad things will happen if this is not done.
have to + infinitive
must + infinitive

3. HAVE TO: (strong obligation)
Have to is often used when the speaker feels a requirement or we use have to when the speaker feels that something is necessary.
I have to study today. (there is a big test tomorrow)
I have to go to the doctor. (I am in a lot of pain)
You must exercise. (doctor says)
You must be quiet. (teacher says)

4. HAD BETTER: (threat/warning)
Had better is often used as a threat or we use had better when the speaker feels there will be problems if something isn’t done.
I had better pay my electric bill. (they are going to turn off the power)
I’d better go to the doctor. (I am in a lot of pain)
You had better quit smoking. (doctor says)
You’d better be quiet. (teacher says)

5. Must not :
Must not is used to express negative obligation (an obligation not to do something ) Or We use must not to say that something is a bad idea .
You must not drop those glasses . They’ll break .
You must not wear your best clothes . You’ll get them dirty .

6. Negative And Question Form:
Negative form : “don’t/ doesn’t have to” means no obligation , It’s OK if you don’t. Question form : Do/ Does +subject + have to + verb + ….
You don't have to eat anything you don't like.
I don't have to work on Sundays.
Do I have to do it for Monday ?
Does she have to work for Sunday ?

7. Must:
+ : subject + must + verb +….
- : subject +mustn’t+ verb+ ….
? : not used
Must use in present tense but must has no past tense form , so change to “had to” (past form of “have to” ).

8. Have to :
*Present :
Have / Has to - don’t/doesn’t have to - do / does … have to
*Past :
Had to – didn’t have to – did … have to –
*Future :
For future with “will” only use “will have to”
not Will must

9. Advice And Recommendation :
"Should" is most commonly used to make recommendations or give advice. It can also be used to express obligation as well as expectation. Examples: When you go to Seoul, you should visit Gyeongbok Palace. recommendation You should focus more on your family and less on work. advice I really should be in the office by 8:00 AM. obligation By now, they should already be in New York. expectation

10. Advice And Recommendation :
Should + p.p. verb:
We use these forms when someone didn't do the right thing.
Example :
We didn’t play very well . We should have played better .
I got lost .~ sorry . I should have drawn you a map .
It was a lovely old building . They shouldn’t have knocked it down .

11. Discussion Questions
What do you use the most energy for? Explain and give examples.
What appliances do you use most often?
Which appliances do you use that use the most energy?
What are some ways that you try to conserve energy?
What are some ways you could conserve more energy?
How do you and your family help the environment?
What do you think is the most serious environmental problem in the world today?
What should we do about it?
What is the most serious environmental problem in Korea today?
How do you think Kyonggi University can help protect the environment?
What do you think are the best forms of renewable energy?

12. Homework
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