I have learned that "if" is used for more or less likely possibilities while "when" is used for things which are considered facts.
Now I read a bit similar to the following in a book.
My sister had stolen my beer. Last time, my brother had taken it, and I would have expected this to be the case now, too. If it was my sister who took it it was because of the bad example my brother had set.
It has been made clear by the text before that my sister has taken the beer, so there is nothing "if" about this part, as far as I can tell.
- Is it common to use "if" that way?
- Is there a name for it/or what it does here?
The original sentence was in a history book and the "if" introduced a historical fact. Unfortunately I can't seem to find it anymore which is why I came up with this rather mundane example. But I do know for a fact that my sister took it.