1. PERMISSION, OBLIGATION AND
NECESSITY

2. THROUGH MODAL VERBS
• CAN, MUST
Ex.: We can’t/mustn’t smoke in class
• SHOULD, OUGHT TO (not so strong)
Ex.: We should/ought to do the English
homework.
We should/ought to have read more English
books. (when we regret something we didn’t do in
the past)
• HAD BETTER/HAD BETTER NOT (stronger, a
warning for the immediate future)
Ex.: You’d better not be late for the wedding.

3. THROUGH HAVE TO/ HAVE GOT TO
• HAVE TO: in all cases
Ex.: Students have to do an exam at the end of
the year.
• HAVE GOT TO: more colloquial, for specific
occassions (not general obligations)
Ex.: I’ve got to study for tomorrow’s exam.
• NOT HAVE TO: lack of necessity (not
obligation).
Ex.: We don’t have to wear a uniform at
school.

4. NECESSITY
• NEED TO/DON’T NEED TO: in all cases.
Ex.: I don’t need to wear glasses.
• NEEDN’T+INFINITIVE WITHOUT TO: on specific
occasions.
Ex.: You needn’t bring anything to the party.
• NEEDN’T HAVE+PAST PARTICIPLE/DIDN’T NEED
TO+INFINITIVE: You did it but it wasn’t necessary.
Ex.: I needn’t have bought/I didn’t need to buy
any wine. I had three bottles in the cupboard!
• DIDN’T NEED TO+INFINIVE: You didn’t do it because
it wasn’t necessary.
Ex.: We had lots of drinks and food at home so we
didn’t need to go to the supermarket for the party.

5. PERMISSION/OBLIGATION:OTHER
EXPRESSIONS
• BE ABLE TO/BE ALLOWED TO: especially with a
form or tense CAN doesn’t have.
Ex.: I won’t be able to come to class tomorrow.
You are not allowed to smoke in the building.
• BE PERMITTED TO: more formal, especially in
announcements, signs for rules, regulations:
Ex.: It’s not permitted to enter after the play has
started. (to be allowed to can’t be used after “it”)
• BE SUPPOSED TO: When the rules are not
normally obeyed:
Ex.: Students are supposed to turn off their
mobiles in class, but most of them don’t.