[Grammar] It can rain tonight.

[beachboy]

Why is it wrong to say "It can rain tonight" (if I'm not mistaken, I have to use "may", "might" and "could, among other modals) to express possibility?

 

[emsr2d2]

Mainly because it "can" rain every day! "Can" is about ability. We don't give weather abilities in this way.

 

[SoothingDave]

It also sounds like you are giving permission for it to rain.

 

[beachboy]

But can't "can" express possibility, like "Dogs can live for 25 years", meaning, it's possible for them to live for 25 years? What about "The murderer can be an out-of-towner"? Wrong?

 

[Raymott]

Yes, the dog sentence is right. The murderer sentence requires 'could'.
"Dogs can live for 25 years" is OK, but "My dog can live for 25 years" is not OK. You need 'could' for the second.
If you mention a specific noun, you need 'could'.