Unusable Prerequisites

Unusable Prerequisites refers to the spells, under the standard system, a wizard must learn but can’t actually cast to access the spell(s) they can cast. The standard assumption is this is done by the wizard studying the underlying magical theory and knowing how to go through the motions of casting – and on a good day, might even be able to create ineffective, sputtering, partial effects. This assumption is built into Partially Limited Magery, Limited Colleges Magery, and One-Spell Magery
==Negation==
It is negated by the No Prerequisites Needed (+30%) enhancement on Magery.
==Alternatives==
It mentions GMs might prefer to handle things differently, like locking limited-magery casters from learning certain spells in their college with outside-college prereqs.
An alternative, in justifying the problem ("How can a wizard be said to know or understand a spell that he has never cast?") is assuming they cast it in High Mana places (where Magery 0 is not required to cast).
This however, is not a complete explanation, because High Mana only stands in for Magery 0 for colleges, it does not explicitly fulfill requirements such as needing to know Magery 1, Magery 2 or Magery 3.
Due to that, the "ventured briefly into High Mana" explanation doesn't help with things such as those with Magery 0 / Magery 1 being able to assist with Enchantment, given that Magery 2 is a prerequisite for the Enchantment spell, and it's implied those with less than Magery 2 can supply (minimum 1) energy to enchantment as assistants, even though Assistants must know the enchantment spell.
Changing Prerequisites could offer one path to that, perhaps requiring even more skills known other than magery.GURPS Thaumatology p 32
Another might be in using GURPS Powers rule Using Abilities at Default to gain magery based on some other advantage, or using Extra Effort to temporarily boost magery levels.
As a leveled ability Magery 2 is +100% to Magery 1.
Magery 0 might be thought of as "Magery 0.5" for purposes of extra effort, since it costs half as much as one level of magery. Ergo +100% to get to Magery 1, +300% to get to Magery 2.
A simpler explanation might just be that mages who DID at one point have Magery 2 but don't have it at time of enchantment. could be victim to
#Suspend Magery or Drain Magery
#Crippled Abilities
#Negated Advantage
#Switchable Magery, which might be switched off to avoid Temporary Disadvantages
#switchable-esque Magery such as that taking Preparation Required, Costs Fatigue, Limited Use, Unreliable etc.
#Day/Night aspected magery
Basically you had Magery for learning Enchant in the first place, but not actually for having it usable at all times. Similar as if the magery had been drained temporarily in situations where it was not usable.
One-College magery is not an explanation since it would be on both for learning an Enchantment-College spell AND for casting it, at all times.
Enchantment-Only Magery is explicitly different from One College Only (Enchantment). Presumably someone could take both. Someone who can't cast an enchantment spell could presumably still ASSIST the caster.GURPS Thaumatology p 24
To reflect someone who can lead the enchantment of items but not cast them might be either/or which is 0.3*0.4=0.12
"you can learn spells from any college – even those with Magery prerequisites – if you have enough levels of (limited) Magery"
It might be that EOM only subs for prereq purposes, but doesn't establish a Magery-per-day rate of 2+ since that might be based on what can actually be cast (channeling energy).
Ceremonial Magery has the same value as One College Only which is weird because Ceremonial is a lot more useful (you can cast all enchantment spells normally, and ALSO cast all other colleges ceremonially). It may be that OCO:Enchantment is meant to be taken atop this for a total of -80%.
==References==
*GURPS Thaumatology p 26
==see also==
*Missing Prerequisites
*One College Only
Category:Rules