Unit 7 – Modals of obligation and ability

We often use modal verbs to talk

about obligations and ability.
Let’s look at:
1. When we use (don’t) have to, must(n’t) and should(n’t).
2. When we use can(’t) and could(n’t).
3. How we use these modal verbs to talk about obligations and ability.
4. When and how we use make and let.

When do we use them?

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 Function: When do we use them?
What did the tour guide say about Alex! Weren’t you listening?
the trip to the ancient ruins?
OK. The bus leaves at 8.15am, so we
Yes, but she spoke so fast! I didn’t must be at the hotel entrance by eight.
understand everything. You don’t have to bring lunch, but you
Anything else? Thanks! should bring water as it gets hot.
We must be at the
hotel entrance by Yes. Everyone has to bring a
eight. You should bring We mustn’t touch any photo ID to get in, and we
You don’t have to water as it gets hot. of the ruins. mustn’t touch any of the ruins.
bring lunch. Everyone has to We can leave bags We can’t take photos in the
We can’t take photos bring a photo ID. and things on the bus. museum either. We can leave
in the museum. bags and things on the bus.

allowed not allowed necessary/ not necessary Giving advice

obligatory
Look at the
conversation
and put the
phrases in
bold in the
correct place
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 Function: When do we use them?
have to
Everyone has to bring a photo
1. We use have to when something is necessary, for ID.
example when someone tells you to do something.
2. We use don’t have to when something is not necessary. You don’t have to bring lunch.

must
1. Like have to, we use must when something is necessary We must be at the hotel
entrance by eight.
or when we are obliged to do it.
2. We use mustn’t when something is not allowed. We mustn’t touch any of Notice the
the ruins. difference
can
between don’t
1. We use can if something is allowed. We can leave bags on the bus. have to and
mustn’t.
2. We use can’t if something is not allowed. We can’t take photos inside the
should museum.
Remember, we also
use can/can’t to talk
We use should and shouldn’t to give advice or You should bring water as it gets
about general ability,
say that something is a good/bad idea. hot.
e.g. ‘He can ski really
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 Form: have to, must, should and can
Everyone has to bring a photo
The bus leaves at 8.15am, so we must ID to get in, and we mustn’t
be at the hotel entrance by eight. You touch any of the ruins. We can
don’t have to bring lunch, but you leave bags and things on the
should bring water as it gets hot. bus.

has to What form of have to How do we make

add -n’t
do we use with he, the negative of
(mustn’t,
she and it? must, should and
shouldn’t, can’t)
can?
I/you/we/they:
don’t have to How do we make the
negative forms of Look at the examples an
have to? again. After have to, infinitive
must, should and can,
he/she/it: do we use an infinitive
doesn’t have to or a verb with -ing?
What is the past form
of can/can’t?
could/couldn’t

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 Form: have to, must and should
have to must/should
I/You/We/They
have to go
I/You/He/She/It/We/They
positive Remember that
must/should go
He/She/It modal verbs in
has to go the present (and
could for ability
I/You/We/They
in the past) are
don’t have to go
I/You/He/She/It/We/They followed by the
negative
mustn’t/shouldn’t go infinitive.
He/She/It
doesn’t have to go

Be careful with have to:

With must and should we use the
the form changes in
same structure with all subjects:
the third person
I, you, he, she, it, we, they. How do we use can
(he/she/it).
and could?

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 Form: can and could
You can call me anytime.
I couldn’t go on the bike
ride this weekend.
Can you come next week?

Add ‘not’: cannot No. It is a bare

(can’t); could not infinitive.
(couldn’t). How do we I can swim.
make can/could Does the verb
negative? infinitive use I can to swim.
to?

B. We invert A verb
Which question is Look at the examples
the subject infinitive.
correct: A or B? again. After can/could,
(‘you’) and ‘can’
A: You can dance salsa? do we use a verb
to make a
B: Can you dance salsa? infinitive or a verb -ing?
question.

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 Form: can and could
You can call me anytime.
I couldn’t go on the bike
ride this weekend.
Can you come next week?

positive negative question

e.g. You can call me anytime. e.g. I couldn’t go on the bike ride. e.g. Can you come next week?
Where can you go?
subject + can/could + verb subject + can’t/couldn’t + verb (qu. word) + can/could + subject + verb
infinitive infinitive infinitive?
Verb infinitive is what you find in a
We use the same structure with all
dictionary. But remember, it is without to.
subjects: I, you, he, she, it, we, they.
I can swim.
We don't stress the word can in
I can to swim. the positive and question forms.
When do
Listen to how your teacher says
Short answers are always: we use
it:
Yes, I/you/he/she/it/we/they can/could. can’t = /kən/ make and
No, I/you/he/she/it/we/they can’t/couldn’t. cannot (one let?
You can stop.
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 Function: make and let
My brother let me borrow his
camera to take on the trip. It takes Look what he says
amazing photos. He made me here. What
promise to share the best ones expression does he
with him. use to say that
… let me
someone allows him
borrow …
to do something?

1. We use make to say that we make it an

obligation for someone to do something, or
cause them to do it. … made me
And how does he say
promise …
2. We use let to say that we allow someone that someone made it
an obligation for him
to do something.
to do something?

How do we use make

and let?
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 Form: make and let
My brother let me borrow his He made me promise to share
camera to take on the trip. the best ones with him.

an object What comes directly What form of the the infinitive

after let and make? verb follows let and without to
make?

Let’s practise!
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 Practice activities
Choose the correct option in these sentences.

1. We have to/don’t have to/can’t buy a ticket when we arrive because we paid on the internet.

2. A: Can/Must/Mustn’t I leave my bag here? B: No, you have to/can/mustn’t keep it with you.

3. You have to/don’t have to/mustn’t take photos of the artworks, but you have to/can/must buy a postcard in the
gift shop.

4. A: Should we/Must we/Could we take snacks with us? B: Yes, that’s a good idea. You can’t buy any there.

5. They make/let/made us wait in the queue for over an hour. I was quite upset.

6. The teacher couldn’t/must/had to explain the answer to us. We must/shouldn’t/couldn’t understand it by

ourselves.
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