The document discusses the differences between modal verbs such as should, must, have to. It explains that should and must are true modal verbs that do not require auxiliaries, can form negatives and questions directly, and cannot be combined with other modal verbs. Have to is a semi-modal verb that behaves like an ordinary verb by requiring auxiliaries, and it can be combined with other modal verbs. Examples are provided to illustrate the proper uses of should, must, have to in various contexts.

1. Should – Must – Have to

2. Should and Must are real modal verbs, and therefore,
like all modal verbs:
 They are always followed by the “Infinitive without to”.
Should do, Must do
 They are the same for all the pronouns:
I should, he should, it should etc.

3. Should and Must are real modal verbs, and therefore, like all modal verbs:
Do not need auxiliaries. They take direct negative and
question forms
I Should not (Shouldn´t). We must not (mustn´t)
Should I? Must we?
Never combine with another modal verb:
You should can You should be able to…
He will must He will have to…

4. “Have to” is a semi-modal verb. It is like a modal verb because it
fulfils specific function, but it behaves like an ordinary verb in its
formulation:
It is followed by the infinitive “Without to”:
Have to do
It is conjugated according to pronouns:
I have to, he has to, etc.

5. “Have to” is a semi-modal verb. It is like a modal verb because it fulfils
specific function, but it behaves like an ordinary verb in its formulation:
It needs auxiliaries. It doesn´t take direct negative and question
forms
I don´t have to . She doesn´t have to
Do I have to? Does she have to?
It can combine whit modal verbs:
You will have to, he might have to.

6. I believe teachers should have higher salaries.
You look Tired. I think you should have some rest.
He shouldn´t make a rushed decision.
Do you think we should phone her?
What should I say when I speak to him?

7. He should arrive any minute.
He should be long now.
He shouldn´t have arrived by now.

8. You should have been more careful.
I shouldn´t have said that.

9. Note 1:
“Ought to” is a synonym for “should”.
It generally sounds more formal than
“should”, and is less commonly used
particularly in the question form:

10. Note 2:
Should (but not Ought to ) is also express a small
possibility.
- If I should ever go back there, I will not make the
same mistake again.
- Should you need any further assistance, do not
hesitate to contact me. (Formal writing)

11. He is very ill. You must call a doctor now.
We must not (mustn´t) lose the match tomorrow, or
we will be out of the tournament.
This is the best book I´ve ever read. You must read
too.
You mustn´t hesitate to call me if you need help.

12. You must not (mustn´t) use your mobile devices
during take off.
You must not be late for your interview tomorrow.

13. You must be tired after your very long day.
He must have read my letter, because he repeated
exactly what I had written.

14. You have to make an appointment to see him.
She has failed her exam. She Has to retake it.

15. He was very ill, had to call the doctor
immediately.
He was very busy, I Had to make an appointment
to see him.

16. He feels much better now, you don´t have to call
a doctor.
I didn´t have to make an appointment to see
him.
She has passed her exam, she won´t have to
retake it.

17. Note 1:
As you can see, the main difference between “must”
And “Have to” is that “must” is a necessity felt by the
speaker, whereas “have to” is an external obligation or
rule. If this difference is not relevant, you can use
“must” and “have to”, Interchangeably in positive
sentences.

18. Note 1:
However, be careful that in the negative “must not”
Is still a necessity or an obligation “NOT TO” do
something (a prohibition), whereas “don´t have to”,
removes the necessity or obligation.

19. Note 2:
As “must” has no past tense, both obligation and
necessity are expressed whit “had to” in the past.

20. Note 3:
“Need to” is a softer alternative to both, “must” and
“have to”:
- I must/need to finish this tonight, because I want to
take tomorrow off.
- I have to/need to finish this tonight. My deadline is
tomorrow.
- Do I need to finish this tonight? I don´t need to
finish this tonight.

21. Note 3:
You may also come across the modal verb “Need ”. It
is a very common modal verb, and can only be used in
negative sentences and questions:
- Do I need to finish this? = need I finish this?
- I don´t need to finish this = I needn´t to finish
this.

22. Have you had your exam results?
Yes, I've failed biology. I will ………………..…..retake
it in august.
Oh sorry. You ……….. be pretty upset. What about
physics?
I´ve passed that but with very low mark. My teacher
thinks I ……………….retake that too.

23. Have you had your exam results?
Yes, I've failed biology. I will have to (need to) retake
it in august.
Oh sorry. You must be pretty upset. What about
physics?
I´ve passed that but with very low mark. My teacher
thinks I should (Ought to) retake that too.

24. Do you think you ……………………retake it?
No. I strongly feel that I must …………focus on
biology. I …………fail that one. I …………………..get
at least a 8 in biology to study medicine at university.
Did you fail biology last year as well?
No. I passed in last year. I ………………….have passed
it this year too. I just didn´t study enough.

25. Do you think you should (ought to) retake it?
No. I strongly feel that I must (need to) focus on
biology. I mustn´t fail that one. I have to (need to)
get at least a 8 in biology to study medicine at
university.
Did you fail biology last year as well?
No. I passed in last year. I should (ought to) have
passed it this year too. I just didn´t study enough.

26. You ……..have studied enough! You always do.
The exam …….. have been difficult.
No, the exam wasn´t difficult. I was too tired.
I ………………………....... have partied the night
before.
I ………………………have studied instead.
Oh, I see. Well, you are good at biology.
You ……………………...be able to pass it in august.

27. You must have studied enough! You always do.
The exam must have been difficult.
No, the exam wasn´t difficult. I was too tired.
I shouldn´t (Oughtn´t to) have partied the night
before.
I should (ought to) have studied instead.
Oh, I see. Well, you are good at biology.
You should (ought to) be able to pass it in august.

28. I hope so. I ……………….………….find a summer job
as well. My dad insist!
Did you have a summer job last year?
No. I didn´t ……………………. work last summer.
I have some savings then.
What happen to your savings?

29. I hope so. I will have to (need to) find a summer job
as well. My dad insist!
Did you have a summer job last year?
No. I didn´t have to (need to) work last summer.
I have some savings then.
What happen to your savings?

30. I had to buy a car because my flat was too far
from the college.
Well. Good luck with your retake. You must let
me know how it went.