She must be tired. 

Must , Can’t

In the lessons on modal (auxiliary verbs), we have stated that must is used to express necessity and rules. In this lesson, we will see the meaning of “certainty”.

Must / mast /

“must” when it comes to the certainty of a situation:

She has been studying for hours. She must be tired.

This shop sells qualified fabric. It must be very good shop.

He must be very exhausted.He has been working a lot.

They must get excited because they liked the match.

He says he gave the address to me.I must keep it safe.
We are sure you got the message. You must have it.

They must be very pleased because they got the first degree at the chemistry olympics

must have done

A: Where is Jane ?
B: She must have gone to the supermarket

A: I rang the doorbell many times but they didn’t answer.
B: They must have left.

A: He didn’t do his homework for this week.
B: He must have forgotten it.


Can’t was used as the negative of “can – ability” in previous lessons. In this lesson, we will see that it is used for impossible situations.

I can’t know the answer because I haven’t studied much.
You can’t  be joking.
You can’t be tired because you didn’t do anything.

Can’t have done 

They can’t have finished the business.
He can’t have got the email.

The pen you bought is not very good quality. You can’t have paid much money.

Scroll to Top