We often use modal verbs or other modal expressions when we want to express an opinion or attitude about a possible fact or to control a possible action. All modal expressions are about the speaker’s or writer’s view of the world.
We can divide most modal words and expressions into two types of meaning:
The speaker or writer decides how certain something is, either in the present, future or past. They predict or speculate about a fact. We see this type of meaning when we talk about degrees of certainty, possibility, likelihood, doubt:
Eg:Paula can’t be home yet. It’s impossible. She left 10 minutes after us.
[The speaker hears the phone ring and predicts who is ringing.]
There’s the phone. That’ll be Mum.
I may go. I haven’t decided yet.
The speaker or writer wants to control or ‘direct’ the action. They give and refuse permission. They talk about obligation and necessity. They talk about how they would like the world to be:
[parent says to child]
Eg: You can come if you’re good.
He should take more care.
Tell Jen she needn’t bother about the washing up.
You mustn’t worry so much about her.
You may go now. (formal)