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Old 09-06-2013, 11:25 PM   #1
talus
 
Join Date: Sep 2011
Default Magic spell prerequisite count corrections

I've recently been looking at adjusting the prereq counts for a ritual mage in my campaign, so of course I started by writing a script to parse each spell's prerequisites from GURPS Magic and then calculate the minimum number of prerequisites according to the method used in Thaumatology (advantages count as 0). This of course exploded into a multi-week project, but now I'm finally done :).

Out of 837 spells, 33 didn't match my script's results. They fall into three general categories: probable textual errors, 'x different colleges' interpretation (Wish/Great Wish), and apparent bad counts. I manually analyzed most of the differences to verify my script's counts, though I didn't dive into the really big ones (they are left as an exercise for those even more obsessive than I).

I'd like to get some feedback on the differences and some spot-checking on my data. Hopefully this can be put into an errata eventually. Below is my analysis, and I've attached a spreadsheet with the full list of spells and counts from both Thaumatology and my script as well as the calculated list of requirements for each spell (though those are a bit hard to read).

Also, I reviewed the errata @ http://www.sjgames.com/errata/gurps/4e/magic_2.html. If there's additional data elsewhere please point me to it!

Results Spreadsheet (xls/csv):
http://www.dsmall.com/gurps_files/CalcedPrereqsCSV.zip
http://www.dsmall.com/gurps_files/CalcedPrereqsXLS.zip

Out of 837 spells: Found 33 different spells with a total prereq delta of 63.

Summary:

Probable Errata:
  • Homunculus
  • Timeslip Other (VH)
  • Crystal Ball (also calculation error) 13 -> 16 or 8
  • Create Gate (VH)
'x different colleges' related
  • Great Wish (VH) 18 -> 17
  • Wish (VH) 17 -> 16
Apparent Bad Counts:
  • Analyze Magic 3 -> 2
  • Animate Object (VH) 6 -> 5
  • Astral Block 16 -> 15
  • Body of Shadow (VH) 4 -> 7
  • Duplicate (VH) 15 -> 14
  • Effigy (VH) 13 -> 12
  • Essential Acid (VH) 13 -> 15
  • Forest Warning 4 -> 1
  • Geyser (VH) 9 -> 11
  • Hideaway 15 -> 18
  • Inscribe 7 -> 6
  • Know True Shape 9 -> 7
  • Leak 16 -> 19
  • Mapmaker 9 -> 8
  • Remove Curse 13 -> 15
  • Rebuild/TL (VH) 22 -> 23
  • Recall 9 -> 8
  • Repel Spirits 14 -> 12
  • Schematic/TL (VH) 7 -> 6
  • Suspend Mana (VH) 11 -> 12
Unanalyzed, likely calculation errors:
  • Corpulence (VH) 16 -> 18
  • Doppelgänger (VH) 29 -> 31
  • Enslave (VH) 14 -> 15
  • Hide Object 20 -> 19
  • Move Terrain (VH) 29 -> 27
  • Sanctuary (VH) 21 -> 19
  • Wraith (VH) 24 -> 25

Details:

Probable Errata:
-----------------------------
Homunculus : (15->5) "Magery 2 and Mind-Sending."
Probably a typo in the prereq string: should it also require Enchant? If so, then the count is correct.

Timeslip Other (VH): (7->6) "Timeport."
Probably a typo in the prereq string: Timeport has 5 prereqs, Timeslip has 6. If it depends on Timeslip then the count is correct.

Crystal Ball : (13-> 16 or 8) "Divination (Crystal-Gazing)."
Possible typo- may also want Enchant (VH). Count off in both cases.
Code:
: Enchant (VH) -> [10 college spells]
: Divination (Crystal-Gazing) -> History -> Trace -> Seeker -> [2 "seek"]
:                                                           -> Seek Machine/TL, Seek Earth
:                             -> Earth Vision -> Shape Earth -> [seek earth]
: [10 college spells] has [History, Seek Earth, Seek Machine/TL] +7 other spells
: calc: 16, or if no Enchant then 8
Create Gate (VH) : (14 -> 13?) "Control Gate. The caster must also know Teleport to create a gate leading to another place, Timeport to create a gate leading to another time, or Plane Shift to create a gate leading to another plane of existence."
This is a single spell, not 3 variants, and Teleport/Timeport/Plane Shift are listed as enabling specific functionality rather than as actual requirements. The wording indicates you can technically learn the spell without any of those, though it would be of very limited use.


'x different colleges'
-----------------------------
This appears to be somewhat inconsistently interpreted. I see three ways of interpreting the variously worded statements:
1) Exclude colleges of any top-level prereqs: Ex. "Lesser Wish and at least one spell in each of 15 different colleges." would exclude all Enchant College spells. This interpretation would change many of the counts from RAW. Also, for Body of Wind, that case is explicitly called out: "Magery 3; Body of Air and Windstorm at 16+ each; and one spell from each of five different colleges besides Air.". Therefore I assume that this is not a correct general interpretation.
2) Exclude only named top-level prereqs: In the example, Lesser Wish (VH) would not be included in the 15 different colleges, but the prereq to Lesser Wish (VH), Enchant (VH), would. This seems to be the most commonly followed (though not for that particular example).
3) Allow top-level prereqs. Ex: Seek Gate: "Magery 2, Seek Magic, and one spell from each of 10 colleges." would only have 10 prereqs, since Seek Magic could count in the 10. This breaks several counts, and doesn't seem to be the designer's intention.

I have assumed that option '2' is correct in my calculations, regardless of minor wording variations. Only Wish (VH) & Great Wish (VH) did not match:

Wish (VH) : (17 -> 16) "Lesser Wish and at least one spell in each of 15 different colleges."
Prereq tree is: Lesser Wish (VH) -> Enchant (VH) -> [10 different colleges]
Enchant (VH) should be included in the 15 different colleges requirement

Great Wish (VH) : (18 -> 17) "Magery 3, Wish, and a combined DX and IQ of 30+."
Adjust as per Wish (VH), above, to 17
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