Past Modals of Deduction

Your friend says the following statement to you:

"I thought I saw Katy yesterday at the library"


If you respond in one of the following ways, how certain are you that your friend saw Katy at the library?

a) “It might have been her, I know she likes going to that library”  

b) “It can’t have been her, she’s in America at the moment!”  

c) “It may have been her, she’s always in there”  

d) “It must have been her, that’s where she works!”  

e) “It could have been her, I know she often goes there during her lunch break”  


Answer these questions related to the above:

Some of the answers above relate to the present.  

All of the answers above relate to the past.  

When we say “can’t have been” or “must have been” we are 100% certain we are correct.  

When we say “can’t have been” or “must have been” we are nearly 100% certain we are correct.  

When we say “may have been”, “might have been” or “could have been” we are saying that it was possible.  

There is a difference in meaning between say “may have been”, “might have been” and “could have been” 


Now you have understood the rules, you can practice with the questions below

She _____ seen me at the party last night, she looked right at me!  

Giuseppe _____ gone to the beach, he hates being under the sun!  

I ____ written down the number wrong, I often do stupid things like that so it’s perfectly possible.  

I did tell you about the dinner tonight, you ____ listening!  

Gaetano ____ been exhausted before the concert last night, as he’d worked for 12 hours straight beforehand!  

Yes, it ____ been better to change the formation during the match, but we will never know!  

Crazy Craig ___ killed Terrible Terry, he hated him and he had blood on his shirt!  

He ___ gone shopping, I remember he said yesterday he needed a new pair of shoes, but he also said he wanted to go skateboarding so I don’t know where he is.  

They ___ been at the market, but I didn’t see them. It’s a very big market though.  

It’s not possible, you ___ seen her – she was sitting next to you!