This document discusses modal verbs and expressions related to permission, obligation, necessity, and ability in English. It categorizes different modal verbs and expressions based on whether they indicate strong obligation, mild obligation, lack of obligation or prohibition, permission or obligation, and ability. Key modal verbs and expressions are defined for each category with examples.

1. PERMISSION, OBLIGATION,
NECESSITY, ABILITY
Modal verbs and related
expressions

2. STRONG OBLIGATION
• MUST (often for personal, internal obligation)
Ex.: I must study hard today
• HAVE TO (have got to, more coloquial): in all cases, but
preferred for external situations, laws, etc.:
Ex.: Students have to do an exam at the end of the year.
• MAKE+SOMEONE+VERB (INFINITIVE WITHOUT TO)
Ex.: The teacher makes us read a book to pass the course.
• HAD BETTER/HAD BETTER NOT (a warning for the
immediate future)
Ex.: You’d better not be late for the wedding.

3. MILD OBLIGATION
• SHOULD, OUGHT TO (not so strong, advice)
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)
• 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.

4. LACK OF OBLIGATION, PROHIBITION
• NOT HAVE TO: lack of necessity (not
obligation).
Ex.: We don’t have to wear a uniform at
school.
• MUSTN’T/CAN’T: prohibition
Ex: You mustn’t/can’t smoke in class.

5. PERMISSION/OBLIGATION:OTHER
EXPRESSIONS
• BE ALLOWED TO/ALLOW TO:
Ex.: You are not allowed to smoke in the
building.
• CAN/MAY + LET (someone)+INFINITIVE
WITHOUT TO:
Ex.: You can/may go to the party/I’ll let you go to
the party.
• 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”)

6. ABILITY
• CAN:
Ex.: I can speak English really well.
• BE ABLE TO: especially with a form or tense
CAN doesn’t have.
Ex.: I won’t be able to come to class
tomorrow.
• WAS ABLE TO/MANAGE TO: for a single
occasion in the past (conseguir):
Ex.: I managed/was able to finish the
marathon.