Copyright 1997, 1998, 1999, 2000, 2001, T. Bone, tbone@gamesdiner.com. All rights reserved. GURPS is a trademark of Steve Jackson Games, Inc. Copyrighted material appears courtesy of Steve Jackson Games.
GURPS is funny in that there are skills for each and every specific specific application of magic (i.e., spells), but no skill to cover a mage's overall understanding of magic itself.
Create a skill named Magic (M/VH, with bonuses from Magery and the same bonus as spells from Eidetic memory). It's learnable only by mages and defaults to IQ-6.
The skill lets you "fine-tune" magic in your campaign, in any one or more of the following ways:
1) Use Magic as a mage's roll to sense magic. In GURPS, the most experienced, ancient mage has the same base roll (IQ+Magery) to sense magic as does the greenest apprentice. Granted, ol' Merlin's IQ is probably higher, but shouldn't experience count for something?
Use Magic instead, and the crusty old wizard's years of experience do indeed make a difference. Meanwhile, the newbie who hasn't yet learned he's a mage will have just enough default Magic skill to sense odd things once in a while, far less than he'll sense once he actually receives instruction.
2) Use Magic as the "research roll" for creating new spells and the such. This makes a lot more sense (under most fantasy campaign concepts of magic) than using the same (IQ+Magery) base roll for both ancient mages and newbie casters.
3) Use Magic to limit spell levels: no spell level may be higher than Magic. This keeps mages from buying up one spell to abusive levels too cheaply.
4) Let non-mages learn Magic, at a hefty penalty, for a world in which only a chosen few (the mages) are truly skilled with magic, but anybody might learn a spell or two with great effort. This option presumes 3) above is in use; non-mages' low Magic skill is what will limit their spell levels.
5) Make Magic-12 a prerequisite to learn spells. For spells you want to control, set higher levels of Magic as a prerequisite.
6) Allow Magic to substitute for levels of Magery needed to learn a spell. For example, Magic-20 might let a Magery 1 wizard study and learn a Magery 2 spell, etc.
Alternately, for each level of Magery below that required to learn a spell, give the learner a -5 or so to Magic and spell skill with regards to that spell. The Magery 1 wizard could learn a Magery 2 spell, but at -5 skill (and can't learn it past Magic -5). This ties in with 4) above, if you consider non-mages as having Magery 0.
So go ahead and learn those spells they told you you couldn't handle! With something as infinite as magic, shouldn't grim determination be able to overcome limitations?
7) Use Magic for any other rolls to test "understanding" of magic. With rolls against both Magic and the spell being cast (and probably extra casting time), you could insert a bit of the "improvisational" magick from GURPS Mage, allowing PCs to tweak standard GURPS spells in minor ways.
8) If you feel that the added requirement of Magic skill is too harsh on mages, let Magic include some freebie, such as skill in one spell (Aura is a good candidate), or let Magic/10 add to all spell levels, as Linguistics does to languages.
But improveable Mage Sight and "research" rolls are really benefit enough for the point cost of Magic.
9) Use Magic as a wizard's skill with the "language of magic", should it be necessary to know that. (Obvious use: can Zartoff read that scroll he's found? Now we have something to roll against.)
10) Call this skill Thaumaturgy, and hey, it's in GURPS Grimoire! Read the description there, and add any of the ideas above that you like.
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