A: Do you know where John is?
B: No, I don't. He might be on a break.
Certainty
If we are less than 100% certain about a situation, we can use modal verbs to show our level of certainty:
|
100% certain |
He is on a break. |
|
|
Almost 100% certain |
He must be on a break. He has to be on a break. He's got to be on a break. |
Must means you are very sure, but not 100%. Although not modal verbs, have to and have got to can be used as the same meaning of must, especially in North American English. |
|
Uncertain |
He may be on a break. He might be on a break. He could be on a break. |
May, might, and could are used to say that you are unsure. |
He must be hungry. He hasn't eaten anything all day.
She has to be here. That's her headset.
She has to go home early. She might have to do her flight physical.
In negative situations, we say the following:
|
100% certain |
He isn't here. |
|
|
Almost 100% certain |
He can't be here. He couldn't be here. |
Can't is commonly used to express a strong certainty that something is impossible. Couldn't is used in the same way, but is somewhat less common. |
|
Uncertain |
He may not be here. He might not be here. |
May not and might not express uncertainty. Notice could is not used for this meaning. |
She joined the Air Traffic Control school this morning, so she can't know the rules of the school yet.
You said Joe was Canadian, but he speaks English with an Irish accent. He can't be Canadian.
Jose may not understand what you are saying. His English is not as good as mine.
Continuous Forms
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