1. Modals - Possibility

2. Modals - Possibility
The following modal verbs can be used to express possibility:
You use ‘can’ to say something is possible.
You use ‘could’, ‘might’ and ‘may’ to indicate that you are not certain something is possible, but you think it is.

3. Modals - Possibility
When you want to say that something is possible, you use ‘can’.
Playing tennis can be a real pleasure.
Sometimes this can cause problems.
You use ‘cannot’ or ‘can’t’ to say that something is not possible.
This cannot be true.
I can’t be there on time.

4. Modals - Possibility
If you want to indicate that you are not sure whether something is possible, but you think it is, you use ‘could’, ‘might’ or ‘may’. There is no important difference between these modals, but ‘may’ is slightly more formal.
That could be a good idea
He might do it.
He may show up.

5. Modals - Possibility
You can also use ‘might not’ and ‘may not’ in this way.
He might not be at home at all.
They may not graduate from school this year.
Note: ‘could not’ normally refers to an ability in the past and not to a possibility.

6. Modals - Possibility
When there is a possibility that something happened in the past, but you are not sure, you use ‘could have’, ‘may have’, or ‘might have’, followed by a past participle.
It could have been tomato soup.
You may have noticed this advertisement.

7. Modals - Possibility
You can also use ‘might not have’, or ‘may not have’ in this way.
He might not have seen me.
They may not have done it.

8. Modals - Possibility
You use ‘could not have’ when you want to indicate that it is not possible that something happened.
He didn’t have a boat, so he couldn’t have rowed away.
The answer couldn’t have been wrong.

9. Modals - Possibility
You also use ‘could have’ to say that there was a possibility of something happening in the past, but it did not happen.
It could have been awful. (But it wasn’t awful.)
You could have got a job last year. (But you didn’t get the job.)

10. Modals - Possibility
You also use ‘might have’ or ‘could have’ followed by a past participle to say that if something had happened, then there was a possibility of something else happening.
She said it might have been all right, if the weather had been good. (but the weather wasn’t good, so it wasn’t all right.)
If I’d been there, I could have helped you. (But I wasn’t there, so I couldn’t help you.)

11. Modals - Possibility
‘Be able to’, ‘not be able to’ and ‘be unable to’ are sometimes used instead of ‘can’ and ‘cannot’, for example after another modal, or when you want to use a ‘to’- infinitive, an ‘-ing’ form, or a past participle.
When will I be able to pick them up?
He had been unable to get a ticket.

12. Modals - Possibility
You use ‘used to be able to’ to say that something was possible in the past, but is not possible now.
Everybody used to be able to get free eye tests.
You used to be able to buy cigarettes in packs of five.

13. Modals - Possibility
Note: You also use ‘could’ followed by a negative word and the comparative form of an adjective to emphasize a quality that someone or something has. For example, if you say ‘I couldn’t be happier’, you mean that you are very happy indeed and cannot imagine being happier than you are now.
You couldn’t be more wrong.
He could hardly have felt more ashamed of himself.

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