Modal Verbs and their substitutes
Modal verbs are for example may, can, must, should, need. They express an ability, permission, wish etc. to do something. (I may, can, must swim.) Many modal verbs cannot be used in all of the English tenses. That`s why we need to know the substitutes to these modal verbs.
Modal Verb
Substitute
Example

must
to have to
I must swim. = I have to swim.

must not
not to be allowed to
I must not swim. = I am not allowed to swim.

can
to be able to
I can swim. = I am able to swim.

may
to be allowed to
I may swim. = I am allowed to swim.

need
to have to
I need to swim. = I have to swim.

need not
not to have to
I need not swim. = I don`t have to swim.

shall / should/ ought to
to be supposed to / to be expected to / to be to
I shall / should / ought to swim. = I am supposed to swim. / I am expected to swim. / I am to swim.


Exercise on Modal Verbs and their Substitutes
Choose the correct substitute for each modal verb.
We ought to win the race. → We
win the race.
I can swim. → I
swim.
You must meet my best friend. → You
meet my best friend.
He should be in bed by now. → He
be in bed by now.
I must get up early. → I
get up early.
They may stay up late. → They
stay up late.
She needs to see the doctor. → She
see the doctor.
We need not walk. → We
walk.
You must not sleep → You
sleep.
Should I go to the cinema with them? →
go to the cinema with them?
Exercise on Modal Verbs and their Substitutes
Use modal verbs where possible. If a modal verb can`t be used with a certain tense, use its substitute.
You (must)
get up early tomorrow.
You (not / need)
call a baby sitter.
We (may)
watch the film tonight.
He (not / can)
see me yesterday.
She (must)
stay at school yesterday afternoon.
(may / you)
go to the disco yesterday?
He (not / must)
sleep now.
You (not / need)
answer.
He (ought to)
give evidence at the court yesterday.
Since he bought the new car he (not / can)
sleep.