Intermediate grammar exercise: positive and negative forms of modal verbs

English grammar practice exercise, for intermediate learners.

In this exercise you will practise modal verbs in their positive and negative forms.

Exercise instructions

Complete each sentence using one of the following modal verbs:

can, can’t
must, mustn’t
needn’t
have to, don’t have to
.

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Modal verbs: negative forms
positive negative
can (used for possibility)
It can happen; everything's possible.
can't (cannot)
It can't happen; it's impossible.
can (used for permission)
Can I smoke here? ∼ Yes, you can.
can't (cannot), mustn't
You can't smoke here. You mustn't smoke here.
can (used for ability)
I can play the guitar.
can't (cannot)
I can't play the guitar.
must, have to (used for obligation)
You must be there at 8 o'clock.
You have to be there at 8 o'clock.
don't have to, needn't
You don't have to be there at 8 o'clock.
You needn't be there at 8 o'clock.
must (used for personal opinion, certainty)
He must be here somewhere – his car is outside.
can't (cannot)
He can't be here – his car's not outside.
might, may (used for personal opinion, certainty)
He might/may be late today – there's a lot of traffic on the roads.
may not, might not
He might/may not get here on time – there's a lot of traffic on the roads.
should (used for weak obligation / advice)
You should stop smoking because it's unhealthy.
shouldn't (should not)
You shouldn't smoke so much – it's unhealthy.