This document discusses the use of modal verbs and other expressions to indicate permission, obligation, and necessity in English. It explains how "can, must, should, ought to, had better, have to, have got to, need to" are used to show different levels of obligation or necessity. It also covers expressions like "be able to, be allowed to, be permitted to, be supposed to" and their appropriate uses depending on whether referring to specific occasions, general rules, or acknowledged but unenforced obligations.

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.