Sometimes people will be unsure of something they think might happen. They will then say "if and when it happens, we need to be prepared" or some such thing. I have never understood what this is supposed to mean. If they just said, "when it happens...", then they would have been assuming that it would happen, when it might not happen. My guess is that somehow, to avoid that impression, someone started saying "if and when...", and then they were sure to have covered all their bases. The only problem with this is that you can do that simply by saying "if it happens...", because that allows for both possibilities -- its happening and its not happening. So were the people who first started using this odd conjunction simply unaware of that?
What's worse is that they made it a conjunction rather than a disjunction. If they thought of 'if' and 'when' as two distinct possible introductory connectives, then they should have said "if or when...", but that's not what people say. What is 'if and when' even supposed to mean, then? I think it just means the same thing as 'if'. I think it also means the same thing as 'if or when'. It's a strange sort of redundancy, though, because it's not analyzable in terms of its components as 'if or when' would be (though that's redundant also, just a more easily analyzable redundancy). So what's going on here? When annoying expressions are as commonly used as this one, it's a great relief when someone can explain them in a way that makes them much less annoying, but no one's ever done that with this one. Is there something I'm missing?