Why the base of unseen arm is 2 insteaad of 3? (example to move a bag of coins -> 1 + 2 of metal)
I think that the best answer is: because it's a legacy spell (a spell from previous editions, that had that same level in previous editions, and that the ArM5 writers tried to "fit in" the new spell guidelines framework as seamlessly as possible).
If you want a more "rule-wise" justification, I think that:
- with base 1 (natural movement) you can make things happen that someone who was watching carefully would still assume a coincidence. E.g. loosen a knot, make a door slowly swing open.
- with base 2 (slightly unnatural movement) you can make things happen that could go unnoticed if no-one was watching carefully. This usually entails moving small stuff slowly. E.g. slowly shift a cup along a table or from a stool up onto a nearby table, strum the strings of a lute.
- with base 3 (highly unnatural movement) you can both move bigger stuff, and move it more freely. Stuff that can't go unnoticed, even if one isn't paying attention. E.g. juggle three daggers, make a chair dance around.
Perhaps we need to use the same solution used for other legacy spells, "This spell is derived from pre-Hermetic magic, and does not strictly fit Bonisagus's theories."
Actually, the Base is problematic not because of the type of movement, but rather because of the type of material.
Thus it seems that, in order to move "anything", you would need to use the higher magnitude modifier, making the spell Base 3.
The typical, simpler solution for such legacy spells in ArM5 is on Experimentation: Extraordinary Results. Namely
If the legacy spell's level is found to be a magnitude off the guidelines, then its authoritative first inventor did experiment on it, and its effects got modified. And once the first Mastery Tractatus and lab texts on it were distributed, the spell was established as is now.
Cheers
I thought boosts from experimentation change the resulting spell level, not that they alter baseline - precisely to avoid having optimised baselines and normal baselines. As that can be confusing.
Yep. And Unseen Arm is a spell, not a baseline.
Cheers
Not what I meant. The experimentation results in a free boost which still uses the correct guidelines and does not provide a spell which is inconsistent with the cannon.
It is better to say that the spell is slightly non-hermetic.
I think it's easier to just rule that either the spell or the guideline is in error, rather than come up with another non-hermetic exception.
It's not really clear to me why moving gemstones is harder than moving rocks anyway. Should semi-precious gems get a half a magnitude?
Experimentation changes the final level only if the sg is a dick and/or the player is a massochist.
A reasonable interpretation is that the effect itself gains (or looses) power, without altering the intended level. otherwise one can roll a seemingly positive result that ens up in a spell you cannot even start inventing and the whole season is wasted because of a good roll.
Also, an "Experiment" is a much more aesthetically pleasing (and simpler) excuse as opposed to running towards "non-Hermetic" for each and every inconsistancy.
Pplease do not take offense to my smarmy smart mouth. I mean no offense to anyone specific or in general.
Having said that, Ars Magica has ever been prone to killer DM's and unduly restrictive interpretations/additions.
Ironboundtome,
I use (and will always use) that when you obtain a resulting spell from experimentation, you can have a spell effect which doesn't match his level. That's fine.
Sometimes it will be good, and maybe become "public knowledge" (like the unseen arm in this example), sometimes it will be detrimental and useless (like a spell level 10 doing less than the level 5 version because of experimentation failure).
In either case, experimentation should never change the level (it's also implied in the "modified totally" result of the chart - serf's parma -) because of the possible issue Marko explained: inventing sometimes you wouldn't be able to... resulting in a failure on a good experimentation roll. or, even if you decide that the magus could invent it, maybe it is something he cannot cast while he would have been able to cast the "expected" level result...
Indeed.
Ironboundtome is not always understandable to me here, but AFAICS his preoccupation is with baselines as foundations for further research and/or experimentation. And there I can follow him.
If he wishes to change the level of the spell or effect invented by experimentation in his campaign, he needlessly runs his players into all kinds of trouble.
But if he wishes to prevent such spells or effects off the guidelines from further being improved upon by experiments, this is sound and consistent.
Calling them non-hermetic or off-canon is an unnecessary exaggeration risking to add confusion.
Cheers
I've taken the approach I outlined in pen and paper games with beginners and they've followed it. I've also seen but not personally played the way Marko and others suggest - it worked too.
I like my way better for the sake of keeping to guidelines. IDGAD what approach a game uses; they're as problematic as each other. Horses for courses.
I think the spell guidence is not wrong because you move the pouch with the coins and not the coins in a direct way. The pouch is dead worked fur so is terram and not animal. There is a rule you use Terram for worked objects or I am crossing editions.
Actually, the spell mentions the need for the appropriate casting requisite, so moving an object make of leather or fur (such as the pouch in question) would require an Animal requisite IMHO.
Although it does fit the A&A description for terram which also is for solid things. But that control would be very fine to say that a terram spell is manipulating the terram particles in the to do something with it.
Actually, if I'm not mistaken, the pouch of bags is just an example. What the spell description says unambigously:
Further elaborating later on that:
So imagine you want to make a spell to move small gemstones at Voice Range and Duration Concentration. Your final spell level would be ReTe 10 (Base 3, +2 Voice, +1 Conc), where base level is 3 because you are using the level 1 guideline (Control or move dirt in a natural fashion) plus 2 magnitudes for metal or gemstones. Whereas you could instead just settle for a level 5 spell (Unseen Arm) that can move gemstones and everything else, with the exact same Range and Duration.
It strikes me as inconsistent, doesn't it?
Isn´t the most likely answer why the baseline is 2 instead of 3 that the authors made a mistake?
How you handle the mistake is up to the troupe. Errata, legacy spell or experimentation is all valid ways.
It isn´t the only spell in the book that is wrong. Eyes of the Cat MuCo(An)5 should have been T:part and therefore level 10.
I'd argue that T:Ind is correct, but there should be no the Animal requisite 
(MuCo Base 2: "change someone to give them a minor ability" -- the "cat" part is merely cosmetic)