Modal verbs features: Modal verbs have more than one meaning: I can swim ability

Could have (done) is also used to say that something was possible to happen but didn’t happen:
He was lucky when he fell of the ladder. He could have hurt himself.

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  Couldn’t have (done) is used to say that someone didn’t do something and anyway it wasn’t possible to do it if that person had tried to do it:
  

When I went to New York last year, I decided not to stay with Linda. Later I found out that she was away while I was there, so I couldn’t have stayed with her anyway.

UNIT 10. PROBABILITY

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  When we are sure about some probability must is used in positive and can’t is used in negative:
  

Peter must be in the library, he can’t be at home.(because at this time he is usually in the library)

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  When we the probability is lower than sureness, when it’s just possible may or might are used:
  

A: Where is Ann?
B: She may be in her office or she might be at home.

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  If the probability is very low could is also possible to use:
  

She could also be in a café.( because sometimes she goes to a café to have a coffee)

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  May and might are also used to express possible future happenings:
  
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  Don’t phone at 10 o’clock I may be meeting the tourists.
  
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  The past form of these modals of probability is:
  

must
can’t
may + have done
might
could

His project is ready today and it’s perfect. He must have worked with his friends. He can’t have done it alone. He may have asked help from the teacher.

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  The continuous form is:
  

must
can’t
may + be doing
might
could

A: What is Tom doing?
B: He must be preparing for exams, he can’t be playing with his friends, because his exams will be tomorrow.

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