[whswhs]

When I was working on GURPS Locations: Worminghall, one of my sources was Láng's Unlocked Books, a study of medieval scholastic ideas about magic, and particularly the passages about which sorts of magic were considered licit and which not. I made use of it as a framework for standard GURPS spell-based magic, but you could apply the legalistic categories to develop your own system out of GURPS Thaumatology, I think.

As I recall the framework, there was natural magic, which involved using the subtle properties of plants and stones and so on; it was essentially permitted. The same for alchemy, which was a specialized form of this. There was image magic, which involved pictures and diagrams and runes that focused the magical emanations of the planets and other things; that was seen as questionable but allowable if done by regulated professionals. Then there was magic that involved calling on spirits, and that was always illicit, because the invocation was similar to prayer, and the offering of compensation for their services to sacrifice, and thus it was too similar to worship of false gods. In particular, divination by calling on spirits was always illicit, but divination more generally was illicit if it revealed things distant in space and time, because it trespassed on God's omniscience. On the other hand, dreaming, or interpreting dreams, had obvious scriptural precedent and was allowed.

Path and Book magic seems to be conceived as primarily a form of spirit magic, and might thus be prohibited; but other forms might not be.