certainty, probability, possibility
can; could; may; might; should/ought to, must
Tammekänd, L. 2009. National Exam in English
- We use will to express a strong possibility that something is true, especially when we don’t have actual evidence at the moment.
That will be Maria on the phone - she said she’d call.
- We use must to express complete certainty.
That must be Maria on the phone - she’s the only person with my new number.
- We can always use had to be meaning “must have been” to express certainty in the past.
She had to be the person I saw on the train.
- We use can/could or will/would to form questions.
Who can that be on the phone?
Who would have phoned so late?
- We can use modals of possibility to refer to the past, present or future.
Don’t drink it - it could/may/might be poisonous. (= present; I'm not sure about poison)
It can’t/could/may/might have been poisonous. (= past; ... but luckily it wasn't.)
We may/ought to/might/should get a reply tomorrow. (= future)
- There is sometimes a change in meaning.
It may have/might have rained. (= I’m not sure)
It could have rained. (= but luckily it didn’t)
That will be Maria on the phone - she said she’d call.
- We use must to express complete certainty.
That must be Maria on the phone - she’s the only person with my new number.
- We can always use had to be meaning “must have been” to express certainty in the past.
She had to be the person I saw on the train.
- We use can/could or will/would to form questions.
Who can that be on the phone?
Who would have phoned so late?
- We can use modals of possibility to refer to the past, present or future.
Don’t drink it - it could/may/might be poisonous. (= present; I'm not sure about poison)
It can’t/could/may/might have been poisonous. (= past; ... but luckily it wasn't.)
We may/ought to/might/should get a reply tomorrow. (= future)
- There is sometimes a change in meaning.
It may have/might have rained. (= I’m not sure)
It could have rained. (= but luckily it didn’t)
