5081 modals

A. OBLIGATION
•

We use the modal verb MUST for indicate that is necessary to do
something. Ex. I must do my homework.

•

The negative MUSTN’T is used for indicate that we’re not allowed
to do something. Ex. I musn’t drink cola.

•

The verb MUST doesn’t change with he/she/It. We always follow
this structure:
Subject + (Modal Verb) + vb (infinitive) without TO.

•

We can also use the modal verb HAVE TO for indicate obligation
and all its forms. (don’t have to , had to, has to...)

•

Must and Have to have very similar meanings. They both mean
something is necessary.

•

We usually use have to for talking about rules and laws.

•

REMEMBER!. The negative form of have to and must is very
different. (don’t have to and mustn’t).

Other verbs that can give us obligation are HAD TO and COULD.
•

In negative statements COULD (the past simple of CAN) is
COULDN’T and HAD TO is DIDN’T HAVE TO (it follows the past
simple tipical structure.

•

We also use COULD for talking about ability in the past. We use
COULDN’T when we have to talk about something that we
weren’t able to do.

B. PRACTICE.
B.1- Complete the
sentences. Use the modal
verbs.

1) They_____ arrive on time to
work.
2) They ______ be rude to the
public.
3) They_____ wear an uniform.
4) They _____ careful with us.
5) When I was 5, I _____ walk, but

I ______ swim.
6) They _____ study science.

B.2- Choose the correct verbs.

1) You mustn’t/don’t have to study law to be a forensic
scientist.
2) I must/mustn’t spend some time with my parents. I
haven’t seen them for ages.
3) We mustn’t/don’t have to commit crimes.
4) You must/have to take the passport for travelling
to South Africa.
5) I couldn’t / mustn’t swim when I was 5 years old.
6) You must/could check your answers for avoiding
errors.
7) I had to/could drank water, but I couldn’t/didn’t
have to drink beer.


B.11)
2)
3)
4)
5)
6)
B.21)
2)
3)
4)
5)

6)
7)

have to
don’t have to
must
have to
mustn’t
must
don’t have to
must
don’t have to
have to
couldn’t
must
had to/couldn’t