Modal verbs of Probability - Must, Could, May, and Might

Probability means the chances of something happening; Something likely to happen. We use probability modal verbs must, may, might, and could when we are uncertain about something and are making a guess.

 

Must

We use must when we are sure about something. We mostly use must when there is evidence to support the statement but still not 100% sure.

E.g.,

She must be on her way. She told me she left the house.

It must be raining outside. I can hear the sound.

 

Also, in case of must, When we are sure of something that's not happening, we use can't, not mustn't. Mustn’t is not used for probability statements.

Can't, in case of probability, is used to express disbelief.

E.g.,

It can't be Keanu Reeves; he's a celebrity. He won't use public transport.

 

Could

We use could when the possibility is high but not as high as must.

E.g.,

He could be busy. I don't want to disturb him.

 

May/might

We use may when the possibility of something happening is higher than 50%.

We use might when the possibility of something happening is less than 50%.

E.g.,

It might rain tomorrow.

They might not win the match if they keep fighting with each other.

I may not be able to make it to the concert tomorrow. I have a lot of work to do.

 

Past tense

When we are unsure or not 100% sure of something that happened in the past, we use modal verb+have+past participle.

E.g.,

I must have forgotten to bring his notebook.

I can’t have missed the train; I arrived on time.

That was a risky shot. He could have missed the goal.

I may/might have gotten the flu. I can't taste anything.

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