Photos are(were) considered Magic by some people. Yet, we know they are not. Why? Because we know how it works. Knowledge is power and ignorance creates fears, insecurities, religions, magics...
can't remember the author's name who originally said this; "any substancially advanced technology is in distinguishable from magic."
Take a medievil knight and drop him in the middle of, let's say, the bronx. just about everything around him he'll see as a form of magic or as monster or demon, cars for the most part.
I'm not entirely sure if I like the "magic as manupulation of energy" approach. Even though I've only actually seen it used in one place, it seems..... overdone somehow. I was thinking of something more like this:
* All inanimate matter is composed of four elements in various combinations: Earth, Air, Fire, and Water.
* In order of inanimite matter to become animate, it must recieve the fifth Element, Essance.
* Essance is broken down into two distinct polarities, Life and Death.
* Magic is the manipulation of those elements, ether adding them or taking them away (by cancelling them out with another element).
* The Shards are actually the purest, most concentrated form of each element: they give the channeler a supply of that element (mana) to manipulate and perform spells with.
* There are no life/death shards, so the channeler must gain those from the ambiant environment (life and death are very hard to convert from one to the other).
well, scoutdog, you make a good point with your laws. but technically your laws explain more how/why magic works (which is good) where as mine are just basic limitations placed on magic. And consequintly, most of those limitations can't be talked about without throwing the word "energy" around 
Oh here are two more laws i just remembered:
7.) A focal point (power source) is needed for magic to accure. (in this case, a magic book, a staff...a channeler)
8.) A spell cannot be transfered from power source to another. (example: you can't cast a spell from a magic book through your magic staff. same reason why you shouldn't attach a bunch of surge protecters together, it confuses the electrical current into amplifying the power to dangerous levels and cause your connected electrical devices to short circuit.)