You could also set arbitrary limits on what magic is able to do - can't work on living things or only works on living things or only on energy levels (i.e. fireballs, spontaneous combustion, freezing, overloading/draining electrical systems etc) or maybe magic can only affect the minds of other people, like some form of advanced hypnosis that does not require rendering the subject in a receptive/suggestible state and without talking to them (and can be countered with sufficient training).
Work out what you want your wizard to be capable of doing and what, if anything, (s)he needs to do it and how it is done ("Abracadabra" = Earth-Shattering Kaboom
or needs full ritual, "coven" and paraphernalia) and work back from there to effectively eliminate anything else as a possibility. (i.e. if you want to have a fireball fight but not have people turned into toads or time travel/teleportation, have it that magic is purely the manipulation of energy.)
Make it subject to an expanded set of Natural Laws (Thou Canst Not Fuck With Space-time) or derive parts of it from existing laws (Conservation of Energy, Newton's 3 Laws etc). "Can't do that as it would break the law of Thermodynamics. I can, however, do this
I've had to do the same in one of my stories to prevent magic from taking over the whole place and breaking the plot. With the limits on magic, technology is required to do things that magic cannot and people have still got to walk/ride/drive to wherever they want to go.
It's your magic system, you can put whatever constraints on it you please and as long as the constraints are applied consistently and there's a kind of "logic" to it, the reader's will accept it (it's not like anyone's going to be able to turn around and prove you wrong about magic, is it?)
Do it right and it'll seem plausible, an immutable in-universe law and people won't ask "but why didn't they just teleport right into the middle of the fortress and out again?" because they'll know
it's impossible - without any lengthy Hand-Waving
on your part.
In my universe, there's also a world of difference between what "human" magicians can do and deities can do - some of it because the humans just haven't worked out how to do it yet, but they know it's possible (because it's been done by gods/goddesses).
edited 10th Sep '12 4:29:04 PM by Wolf1066