This document discusses different modal verbs in English and their meanings and uses. It explains that must expresses logical deductions or obligations, can't expresses negative deductions, can expresses general possibilities, could/may/might express present possibilities, could/might/would express past possibilities, must and have to express obligations with different levels of emphasis, should/ought to express weaker obligations, need expresses necessity, needn't/don't have to express absence of necessity in present or past, mustn't/can't express prohibition, and could/should/might/ought to express criticism of past actions.

1. Modal Verbs
(Upstream Advanced)

2. Logical Assumptions/Deductions
(+)
 MUST: sure/certain that sth is true
Used in affirmative sentences, it
expresses positive logical beliefs or
deductions:
You have been practising all day,
you must be exhausted.

3. Logical Assumptions/Deductions
(-)
 CAN’T/COULDN’T: certain that sth is
NOT true/real.
Used in negations, express negative
logical assumptions:
That can’t be my husband, he’s in
London.

4. Possibility (General
Possibility)
 CAN+ PRESENT INFINITIVE: general
possibility, sth theoretically possible; not
used for a specific situation.
You can have milk or juice.

5. Possibility (Present)
 COULD/MAY/MIGHT+PRESENT
INFINITIVE: it is possible/likely,
perhaps; used to show sth is possible in
a specific situation.
You should keep that phone number, it
may be useful one day.

6. Possibility (Past)
 COULD/MIGHT/WOULD+ PERFECT
INFINITIVE: refers to the past, sth that
was possible but did not happen:
You might have changed jobs.

7. Obligation/Duty/Necessity(I):
MUST
 MUST: expresses duty, strong
obligation to do sth; sth is essential. We
generally use MUST when the speaker
has decided that sth is necessary:
I must explain what happened.

8. Obligation/Duty/Necessity (II):
HAVE TO
 HAVE TO: expresses strong
necessity/obligation. We usually use
HAVE TO when sby other than the
speaker has decided that sth is
necessary.
The landlord said we have to pay the
rent tomorrow.

9.  NOTE: MUST and HAVE TO have
different meanings in questions.
- Do I have to pay the full amount now?
(Is it necessary for me…?)
- Must I stay for the whole meeting? (Do
you insist that I…?)

10. Obligation/Duty/Necessity (III):
SHOULD/OUGHT TO
 SHOULD/OUGHT TO: express duty,
weak obligation. These are less
emphatic than MUST/HAVE TO:
You should think about it before you
make a final decision.

11. Obligation/Duty/Necessity(I):
NEED
 NEED: It is necessary to.
You need to work until late tonight.
NOTE: NEED can be used as a modal
verb or as a main verb with no change
in meaning:
Need I put more oil in my car?
Do I need to put more oil in my car?

12. Absence of necessity
(Present)
 NEEDN’T/DON’T HAVE TO/DON’T
NEED TO+PRESENT INFINITIVE: it
isn’t necessary to do sth (in the
present/future)
You don’t need to drive me home, I will
take a cab.

13. Absence of necessity (Past)
 DIDN’T NEED TO/DIDN’T HAVE TO: it
wasn’t necessary to do sth. We don’t
know if it was done or not.
He didn’t need to/have to buy the
newspaper.
(We don’t know if he bought the
newspaper or not)

14. Absence of necessity (Past)
 NEEDN’T+BARE PERFECT
INFINITIVE: it was not necessary to so
sth but it was done.
You needn’t have bought bread.
(You brought bread)

15. Prohibition
 MUSTN’T/CAN’T: It is forbidden to do
sth; it is against the rules/law; you are
not allowed to do sth:
You mustn’/can’t use a dictionary
during the exam.

16. Criticism
 COULD/SHOULD/MIGHT/OUGHT TO+
PERFECT INFINITIVE: used to criticise
someone’s actions or lack of action (in
the past): it would have been better if
you had/had not… (past)
You could have been on time for the
meeting.