This document summarizes the uses and meanings of the modal verbs "must" and "have to". It explains that "must" expresses strong personal obligation or prohibition, while "have to" expresses strong impersonal obligation. It discusses their uses in positive, negative, and interrogative forms. It also covers differences in meaning, such as "must" being used for personal obligations like wishes, while "have to" refers to circumstances, laws, or other people's wishes. Examples are provided to illustrate the appropriate uses of each modal verb in various contexts.

1. Modal verbs
of
obligation

2. must
or
have to

3. must
or
have to
modal

4. must
or
have to
indicative
„helping verb‟

5. be careful with
+ive
—ive
?ive

6. be careful with
+ive
—ive
?ive
in both form and meaning

7. form

8. I must go.
I have to go.
+ive

9. He must go.
He has to go.
+ive

10. You mustn‟t go.
I don‟t have to go.
—ive

11. Must she go?
Does she have to go?
?ive

12. -
She had to go.
past

13. meaning

14. +ive

15. I must wash my hair.

16. You must arrive early.

17. must [+ive] expresses
strong personal
obligation

18. personal obligation means:
- dictated by people
- imposed by a 1st or 2nd person
- what the speaker or listener
wants

19. Must is also used in formal
regulations and warnings
Bookings must be made at least
seven days before departure.

20. I have to get up early tomorrow.

21. Policemen have to wear
a uniform.

22. In tennis, you have to hit the ball
over the net.

23. have to [+ive] expresses
strong impersonal
obligation

24. impersonal obligation means:
- dictated by circumstance
- dictated by a 3rd person
- other people‟s wishes
- laws
- rules

25. —ive

26. You mustn‟t smoke in here.

27. You mustn‟t tell anyone.

28. must [—ive] expresses
strong negative obligation
or prohibition

29. We don‟t have to get up early
at weekends.

30. You don‟t have to tell your
parents if you don‟t want.

31. have to [—ive] expresses
absence of obligation

32. have to [—ive] expresses
absence of obligation
—there‟s no need—

33. we can express
the same concept
(with different emphasis)
using „can‟

34. We don‟t have to get up early
at weekends.
We can get up early
if we want.

35. ?ive

36. Must I eat the vegetables?

37. must [?ive] is rare
between adults

38. must [?ive] is used when
children talk to
figures of authority
(parents, school teachers, etc)
with the meaning:
“is it really necessary for me
to do this thing?”

39. you can ignore
must [?ive]

40. Do I have to do my homework
for next Monday?

41. Do they have to book the
exam?

42. have to [?ive] is used for
(almost) all questions about
obligations

43. past

44. I must go to the dentist
next week.
I had to go to the dentist
last week.

45. I must go to the dentist
next week.
I had to go to the dentist
last week.

46. +ive —ive ?ive
must
personal
obligation
I must wash my
hair
negative
obligation
You mustn‟t tell
anyone.
not
used
-
have
to
impersonal
obligation
I have to go to
the dentist.
absence of
obligation
We don‟t have to
get up early.
all
questions
Do I have to do it
for Monday?

47. Practice
1 must go to bed
2 must find out
3 don‟t have to answer
4 has to vote
5 must throw out
6 mustn‟t hit your opponent
7 must come round
8 have to get

48. 9 have to take off
10 must turn down
11 have to pay taxes
12 don‟t have to go to work
taken from Oxford English Grammar Course by
Michael Swan & Catherine Walter

49. http://oald8.oxfordlearnersdictio
naries.com/dictionary/have-to
http://www.englishgrammarsecr
ets.com/musthaveto/menu.php

50. www.davidnicholson.it
adapted by V. Pardo