Clarification/Errata Request: Is Muto shrinking when dealing with different base individuals mandatory, or optional?

Games Discussion Ars Magica
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When using Muto to change one material to another, it is possible to end up with a different amount of material than you started with, depending on the base individuals used in the spell. An example of this can be found in the Muto Terram guidelines on page 154:

The amount of material you can change is limited by the guidelines for each end. Thus, you can turn a cubic pace of stone into a cubic inch of gemstone with a base Individual.

However, there are two MuAu cantations in Apprentices for which this shrinking is stated to be required, Mimic the Christ's Miracle and An Evening's Illumination. These spells must transform a barrelful of water in order produce a cupful or bucketful of a processed liquid:

Changing water into a processed liquid reduces its size, and it takes a barrelful of water to produce a cup-sized amount of wine.
This spells changes water into lamp oil. As earlier, a barrelful amount of water will produce a bucketful of oil.

Some users have extrapolated this shrinking requirement to apply to all Muto Aquam spells, or even all Muto spells in general, so long as a change in base individual is involved. Personally, I think this interpretation is incorrect because it would alter the effect of many spells, and contradicts some errata, but I will go over each interpretation that I have seen.

Applied to All Muto Spells

The spells in Apprentices are the only Muto spells explicitly stated to behave this way, and it would cause a number of other spells to behave very differently than a casual reading of their effect would imply. For example, Rope of Bronze has as targets a plant 1 pace in each direction (27 cubic feet), and a base metal (1 cubic foot). Were we to extrapolate from the spells in Appprentices, casting Rope of Bronze would shrink the targeted rope to a third of its length.

Extrapolating this requirement would also contradict with the errata for Earth That Breaks No More. The pre-errata description of the spell was as follows:

Turns a volume of packed dirt up to one hundred cubic paces into stone.

As a T: Part spell with +1 Size, it was valid to target one hundred cubic paces of dirt (10 times base target 10 cubic paces), but not stone (10 times base target 1 cubic pace is only 10 cubic paces). As per the rule on page 154, this would have only produced 10 cubic paces of stone from 100 cubic paces of dirt. Earth that Breaks No More eventually received the following errata:

Change the description to read "Turns a volume of packed dirt of up to ten cubic paces into stone".

Now the spell's maximum targetable amount of packed dirt no longer exceeds the ten cubic paces on the stone end. Under the interpretation extrapolated from Apprentices, the post-errata spell would only produce up to a single cubic pace of stone, and the +1 to the spell's magnitude for increased size would have no impact and thus be erroneous.

Applied to All Muto Aquam

There are also a few issues with applying this to the entirety of Muto Aquam. First of all, Bag of Teeth can transform an entire base individual of water into a single animal tooth. This is smaller than the base target for animal, which would contradict the proportionality required by Mimic the Christ's Miracle.

The mandatory proportionality would also cause minor problems with spells such as Lungs of the Fish: each breath of water would create more air than one would expect.

Applied to Only Muto Aquam (fluid->fluid) transformations

I can only find one existing spell that would still be affected by this very limited extrapolation, the ritual Strange Tricks Using Canal Contents from Transforming Mythic Europe. It would, however, prohibit the creation of a water-to-wine spell that does not cause the glass of wine to expand into a barrelful of water after it has drunk.

Applied to Only The Spells In Apprentices

Personally, I'm in favor of treating the proportionality requirements of Mimic the Christ's Miracle and An Evening's Illumination as quirks of those particular cantations rather than extrapolating from them as a rule for other spells, either due to a flaw or deliberate design. On the one hand, a cantation learned through repeated casting might not be as thoughtfully designed as a spell created in the lab. On the other hand, making wine that causes the drinker to explode with water fits in perfectly well with other cantations like Curse of the Baby's Bladder, especially if the storyguide interprets the effects of suddenly having the glass of wine you drunk suddenly become a barrel of water as more humiliating than life-threatening.

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As a T: Part spell with +1 Size, it was valid to target one hundred cubic paces of dirt (10 times base target 10 cubic paces), but not stone (10 times base target 1 cubic pace is only 10 cubic paces). As per the rule on page 154, this would have only produced 10 cubic paces of stone from 100 cubic paces of dirt. Earth that Breaks No More eventually received the following errata:

Change the description to read "Turns a volume of packed dirt of up to ten cubic paces into stone".

Now the spell's maximum targetable amount of packed dirt no longer exceeds the ten cubic paces on the stone end. Under the interpretation extrapolated from Apprentices, the post-errata spell would only produce up to a single cubic pace of stone, and the +1 to the spell's magnitude for increased size would have no impact and thus be erroneous.

I think I follow this and it's a good point.
I'm just not sure why the post-errata versions size increase doesn't apply to the stones base individual.
Is that a consequence of the Part target?

Edit: I mangeled the quote tags somehow, sorry.

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The interpretation extrapolated from Mimic the Christ's Miracle cares about the ratio between the base targets, which we can't change. It says that turning water into wine reduces it's size by a factor of (Water Base Target ÷ Wine Base Target). Substitute Water for Dirt and Wine for Stone for Earth That Breaks No More. The post-errata version reduces the maximum amount of dirt targeted, but because a size increase doesn't change the underlying Dirt : Stone conversion ratio, it ends up just producing 1 cubic foot of stone from 10 cubic feet of dirt.

Some people have suggested replacing the magnitude for size with an effect that causes the stone to grow to counteract the shrinking, but that doesn't work either. The MuTe 4 guideline only grows an object to 8 times its previous volume (rather than the 10 times needed), and is also a level higher than the guideline to turn dirt to stone. That would add an extra magnitude to Earth That Breaks No More while still causing shrinking (though only to 4/5ths the volume instead of 1/10th).

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Arkhaic and I discussed this at length along with Callen on the Ars discord and my preference that is most definitely not RaW is that for elemental transformation one always use a 1:1 ratio unless the spell specifically includes extra magnitudes for altering size. To be clear, I wish this were RaW and I feel the choice made was the wrong one and should be fixed and will propose it as a houserule in any future games. First off, there are 3 general Muto Form situations (I include non-living substances of non-elemental Forms to be the same as elemental forms):

  1. Living Being transformed into Living Being
  2. Living Being transformed into an Element or Element transformed into a Living Being
  3. Element transformed into a different type of the same Element (Water to Wine) or Element transformed into a different Element

This 1:1 ratio can easily be accomplished by using only one base individual for the form(s) involved, always the smaller one but each case needs to be looked at a little differently.

Case 1 is a special case and fundamentally different than the others. Transform a person into a crow or shrub or even a tree or horse if the added size mags cover the tree or horse. no errata or changes needed.

Case 2 is more complex:

  • Turn a Person into a bit of mist and they become a human-sized bit of mist.
  • Transform a person to a Stone statue. Maybe my guestimation is wrong here but I think a solid cubic yard is probably large enough in volume to cover a human of Size +1.
  • Transform a person into an Iron statue, you need a size mag (or more if my guestimation above is off) because a size +1 person is larger than a cubic foot in volume.
  • Transform a Cloud into a human and it is a giant but you need size mags on the Corpus base of being size of +1 to cover the size of the cloud you just transformed into a giant.
  • Turn Part of a cloud or fog into a human of up to Size +1, merely add the Part target.

Case 3 is again pretty simple:

  • Turn Water to Poison, Transform a shot glass or thimble of water ("single dose" is the wording in Core but that's not so helpful as a volume and somewhere around those measures is close to 1/10th the next higher step) into the same amount of poison. Want to transform more then you use size mags and it only affects the shot glass or thimble amount possible with poisons.
  • Turn a keg of beer into water it works fine as a keg is smaller than the base individual of beer and other processed liquids. It also works exactly as it currently does when one transforms from a smaller base to a larger base. No edits necessary.
  • Turn a Cloud into a stone you need Size mags to multiply a cubic yard to be at least as large as the cloud.
  • Turn a stone into a cloud you end with a stone sized cloud and might need size mags if it's a really large stone.

If you want case 2 or 3 to result in a shrinkage or growth add a magnitude for size reduction/increase and enough size reduction/increase steps necessary to handle the change.based on the rules found in Hermetic Projects.

Anyway, this is how I wish the Errata went and it is even more restrictive than what Arkhaic is proposing. That said I think Arkhaic's proposal is at least a step in the right direction because requiring the shrinkage but not requiring the increase in size when stepping up is weird and kinda breaks my suspension of disbelief. But even just allowing the shrinkage, IMO, invites so many questions about avoiding MR by mutoing water into wine and people exploding when the wine becomes water again... or whatever dumb thing to make some "killer exploit."

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I believe Mimic the Christ's Miracle is a possible spell, but not necessarily an example to follow. Muto being limited on both sides by the base individual of what it is transformed from and into doesn't mean you need the maximum amount of dirt to get the maximum amount of stone. It just means you have to design your spells taking into account both limits. Conservation of volume is a possibility, but it's not mandatory either. But many spells make more sense with conservation of volume.

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We had a discussion about this in the Fan Grimoire too.

I prefer the interpretation that the max size is limited by both sides, but the volume doesn't change - but that is not how it appears to be as RAW. Christ's Miracle, as well as the MuIg spell to turn fire into a gemstone as examples.

I am envisioning a Structure-momentary spell to turn all of the duke's wine into water, thereby causing a flooding and explosion due to his prodigious wine cellar.

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Well, I would like to make a spell that MuAq a poison into something harmless - but as that would be much bigger than the poison, do you then vomit a barrelful of water or have a barrelful gush out of the holes in your skin where the snake bit? Am I safer trying to turn the poison into a much weaker poison?

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One if the reasons I strongly think the size reduction for going from larger to smaller bases is that we don't see a corresponding free size increases when going from smaller to larger bases.