[color=indigo]1-I don’t know if four of my friends are alive or not.
Can’t this sentence be used in two different contexts.
[color=red]a-Maybe four of them are alive. I don’t have anyone specific in mind. But maybe fewer than four are alive. You tell me: Why don’t you invite four of your friends to your ninetieth birthday and I say: I don’t know if four of my friends are alive or not.
[color=darkblue]b-I have four specific friends in mind and I don’t know if they are alive or not. As regards all the others, I know whether they are alive or not. I have lots of friends who are alive.