Quote Originally Posted by Rantzien View Post
Quote Originally Posted by Ouch! View Post
As such, I generally think defining magic by what it can do as opposed to what it can't can avoid both situations entirely.
I couldn't agree less. Much of what I enjoy about fantasy is the possibilities that are opened by a new world. By defining magic and other supernatural forces as being able to do this and that, but nothing more, you limit the possibilities and, doing that, you enclose the world in a box. You make it predictable.

I absolutely hate the idea of a perfectly defined world, a world where there is nothing new to discover. I don't see the point of a world where there is already an answer to everything. One of the most charming things about even the real world is that we don't know everything, that there are still some mysteries left.
There's a difference between putting your world inside a box and setting down some ground rules. Rowling's only rule was that magic can't bring people back to life. Otherwise, there were very few specifications to its limitations. That aside, the rules for a given system of magic never have to be made clear to the reader. In the end, I just think that explaining away the ending with a vague, "Nobody could have known!" is one of the worst cop-outs ever.

That aside, there are other (and arguably better) ways to be unpredictable without resorting to such an unsatisfying technique as a deus ex machina.