Ritual Magic issue

[Varyon]

I feel there is some usefulness in determining what the intended default was. We know (they’ve already been referenced) there are places in the books that treat “prerequisites” for purposes of determining Ritual Magic casting penalties as referring exclusively to prerequisite spells. Is there anywhere that treats it as including the required Advantages and the like? If not, or if so but the “-1 per prerequisite Advantage” is explicitly referred to as optional, it seems clear the intended default was to just count prerequisite spells, treating other prerequisites as still being required to use the spell. If so, then there’s a clear discrepancy between books, and we’d probably need to get Kromm involved.

FWIW, I feel the “-1 per prerequisite spell, all other prerequisites still necessary” interpretation makes the most sense (and was what I assumed was the default back when I read the option).

[David Johnston2]

Originally Posted by Stormcrow

I was illustrating the problem with that approach, not advocating for it.

And I was failing to see what you were showing. If anything the problem there is trying to base the difficulty of Ritual Magic on prerequisites in the first place. It strikes me as a crude shortcut to completely designing the system. And I love to screw with prerequisite chains anyway.

[Hide]

Originally Posted by maximara

Which as I pointed out before magery is not counted, even in GURPS Magic (...)

After reading the book several times, I think I see your point. Mysteries of the Trade seems to exempt you from knowing the (spell's) prerequisites (F: 163):

As usual for ritual magic, the professional doesn’t actually have to know the prerequisites

And as I see it, you just get a -1 per prerequisite spell listed by your desired spell.

Then, in a very high mana setting you’d have access to a very cheap pool of spells/magic related to your profession (if you are good at it). This way, a bard with Singing-18 could cast many spells starting at SL-12, with negligible investment. Even if you "force" magery as a prerequisite, you get more benefits than deterrents. What a great option for Fantasy!

[maximara]

Originally Posted by Hide

After reading the book several times, I think I see your point. Mysteries of the Trade seems to exempt you from knowing the (spell's) prerequisites (F: 163):

And as I see it, you just get a -1 per prerequisite spell listed by your desired spell.

Then, in a very high mana setting you’d have access to a very cheap pool of spells/magic related to your profession (if you are good at it). This way, a bard with Singing-18 could cast many spells starting at SL-12, with negligible investment. Even if you "force" magery as a prerequisite, you get more benefits than deterrents. What a great option for Fantasy!

You might want to look at the Very High Mana and Society thread where we are kicking around just what effects a very high mana world would have on society. There are some ideas you might find interesting in that thread.

[shawnhcorey]

I have a question about prerequisites in RPM and this seems like a good place to ask it. Create Air has the prerequisite of Seek Air or Purify Air. For RPM, would the prerequisite count be 1 or 2?

[David Johnston2]

Originally Posted by shawnhcorey

I have a question about prerequisites in RPM and this seems like a good place to ask it. Create Air has the prerequisite of Seek Air or Purify Air. For RPM, would the prerequisite count be 1 or 2?

The shortest prereq chain is fine.

[dataweaver]

GURPS Thaumatology is the definitive source for Ritual Magic. According to it, there are two ways to address non-spell prerequisites:

The standard way is to just continue to require them: if you're attempting a spell that has Magery 1 as a prerequisite, then you need Magery 1 to have any hope of succeeding.

An alternative to this is to replace such prerequisites with a further increase to the prerequisite count (at a rate of +1 per ten points worth of required advantages that you'd otherwise have to take).

That's what Thaumatology has to say about it. The explanation given for why two approaches are given is that the first printing of GURPS Magic used the alternative approach. Everything else it has to say about each approach amounts to elaborating on rules provided in earlier books: for instance, Basic Set not only doesn't say that you should add to the prerequisite count if you have an Advantage as a prerequisite; it doesn't say anything about what to do if you have an Advantage as a prerequisite. This “blind spot” in the rules carries over to GURPS Fantasy and its Mysteries of the Trade section: there's an implicit assumption (by way of overlooking) that all rituals under consideration only have spells as prerequisites. I would not take it as an endorsement of the variant method of calculating prerequisite counts as described in Thaumatology.

That said, I have absolutely no problem deviating from the published rules, especially when what I'm deviating from is itself a variant rule, as Ritual Magic is. In particular, I'd tackle prerequisites vs. the default penalty on a case by case basis:

1. Every spell prerequisite either contributes to a ritual's default count or remains as a prerequisite which must still be met before you can successfully perform the ritual; never both.

2. Skill-like prerequisites are assumed to contribute to the ritual's default count unless the GM decides otherwise. Skill-like prerequisites include spells, but also skills and techniques — though in the existing spell list, skills and techniques that serve as perquisites are vanishingly rare to non-existent; I can't think of any off the top of my head. But I could see alternate prerequisite trees for spells that incorporate mundane spells into them.

A good reason to keep a skill-like prerequisite as a prerequisite would be if it has a non-standard prerequisite level: if you're required to take a skill at, say, 15- or 18- to access a given spell, that shouldn't be reduced to “increase the prerequisite count by one”.

3. Advantage-like prerequisites are assumed to continue to count as prerequisites unless the GM decides otherwise, in which case every ten CPs in such perquisites increases the ritual's default penalty by one. Perks usually count as Advantages for this purpose.

An advantage-like prerequisite should instead apply to the ritual's default penalty if the GM wants spells that are gated by that Advantage to be performable at a penalty without the Advantage.