Duplicating the Magic from Fictional settings in GURPS

[gruundehn]

Originally Posted by David Johnston2

The Will and the Word isn't a system. It's just "I can make anything happen I want"

There was a little more than that, you had to be accurate when making your image and you had to have the energy to do what you wanted to do. And, as mentioned, you could never unmake anything.
Thus Belgarath studied for centuries, presumably to make sure that he go it right when he did something. As well as understand things such as the reason for mountains.
It was a system in that you needed to have knowledge as a prerequisite and enough energy to accomplish your intent. But, other than that and unmaking, there was no limits other than you ability to control the forces.