Unit 5: Modals for Necessity (Present and Past)
We use a variety of modals to express necessity. These modals show
the concepts of obligation, advice, expectation, and suggestion.
Obligation
Present
Past
Positive
You _____ take off your
shoes when you go inside.
Negative
You _______ smoke indoors in
Canada.
I _______ buy a gift for the
wedding.
He ________ speak his own language
in English class.
must, must not, have to, can’t, have got to, aren’t allowed to, weren’t
allowed to, couldn’t, had to
 Must: strong obligations, formal rules
 Have to: formal and informal situations
 Have got to: information situations (casually pronounced as “You
gotta…”)
 Will/Going to have to: future necessity Had to: past necessity
 Must not: for something that is prohibited (like “can’t)
 Don’t have to: for something that is not necessary (your choice)
Advice
Present
Past
Positive
You ______ learn the local
customs before you go to
another country.
Negative
You _______ give a clock as a gift in
China.
He ______ responded to
their dinner invitation.
I ________ been late for the party. It
was so embarrassing!
Should, should have, shouldn’t, shouldn’t have, ought to, ought to
have, had better, had better not
 Should/ought to: something is a good idea
 negative form: shouldn’t (“ought not to” is rarely used)
 Had better: if you don’t follow this advice, there will be negative
consequences
 negative form: had better not
 Should have/ought to have: for something that was a good idea in
the past, but didn’t happen.
 Shouldn’t have: for something that happened in the past, but
wasn’t a good idea. (“ought not to have” is rarely used)
 Could/might: Polite suggestions for the present/future
 Could have/might have: Polite suggestions about a past event
Other Uses
1. Be supposed to: for an expectation in the present or past.
Ex. You’re supposed to bring a gift when you go to someone’s house
for dinner. / You aren’t supposed to take a business card with one
hand in Japan.
 Past: “were supposed to” means the action didn’t happen.
Ex. We were supposed to be here at 8 p.m. (But actually…)
“Weren’t supposed to” means the action happened.
Ex. You weren’t supposed to shake hands with her. (But
actually…)
2. “Be to” + base: for a strong expectation (quite formal/strict)
Ex. In many countries, you’re not to address your boss by his/her
first name. / You’re to arrive in class at 9 am every day. Is that
clear?
3. Shall: In Canadian/American English, shall is generally used for
questions regarding advice, but only with “I” or “we”. Ex. A: It’s
getting late. Shall we go? B: Yes, let’s go.
 In this case, you can substitute “should” for “shall”.