3-27. Can: выражение предположений

 
Could (но не can) может употребляться для предположений о будущем:

It could rain this afternoon. (не ‘it can rain this afternoon’)
It could rain later this evening, perhaps. (не ‘it can rain later…’)
I could possibly have a new job soon. (не ‘I can possibly have…’ )

Но can't можно употреблять, выражая негативную уверенность:

It can't be true. (= It is not possible that it is true.)