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I am very confused about the usage of the modal verb ' could'. I wrote the way I understood each sentence.( Underlined parrts) Is it correct?

Who stole the money?

John couldn't be the one.( it is not possible John is the one who stole the money, but at the same time it is possible for him to have stolen the money)

John can't be the one.( It is impossible John is the one who stole the money)

John could have stolen the money.( It was possible John was the one who stole the money)

John could not have stolen the money.( It was impossible John was the one who stole the money)
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Who stole the money?

John couldn't be the one.( it is not possible John is the one who stole the money, but at the same time it is possible for him to have stolen the money) More or less. It's almost the same as the next one.

John can't be the one.( It is impossible John is the one who stole the money) Right.

couldn't be = It would not be possible - weaker

can't be = It is not possible - stronger

_______________

John could have stolen the money.( It was possible John was the one who stole the money) Right.

John could not have stolen the money.( It was impossible John was the one who stole the money) Right.

But I would say that all possibilities and impossibilities are in the present, because the evaluation of the action is in the present. Only the action itself was in the past.

It is possible that John was the one ...

It is impossible that John was the one ...

CJ
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