Penetration Rules

[Vetrenius_ex_Verditu (Vetrenius ex Verditus)]

I like the idea very much of small spells penetrating while high magnitudes ones do not. In game if gives you a multitude of options.

As for any analogy of this you are at a loss! None of us can work magic or has seen magic being worked. -That is, I think so...
So you can use any analogy to stress the "reality" of how it should work.

For me the analogy sits well with the MR being a flat metal piece. The hight of MR resembling its thickness while the casting total resembles the force of another metal piece that is flung against it.
If you use a piece with a small tip it will penetrate (=low magnitude) using a piece with a larger tip it will not as the force per area is too small.

[Marko_Markoko]

@ndkid

My favored analogy is that MR is a kevlar vest, spell magnitude is bullet size, and casting total + penetration is energy. If someone hasn't got any armor on, a shotgun slug, even moving slowing, might blast 'em in half. But once they put on some armor, they're spreading the force of that slow slug over their entire chest, and bullets that put the same amount of energy on a smaller area are more likely to punch through.

This is an excellent analogy!

[LuciusT]

@Marko Markoko

This is an excellent analogy!

All excellent analogies... from the standpoint of 20th century physics, which alas have nothing to do with 13th century metaphysics.

@Arts and Academe

It might seem counter-intuitive to the modern reader, but without a concept of momentum an object's speed bears no relationship to the force that propels it... Further, stones thrown by a strong man do not travel faster than those thrown by a weak man, although they can travel further..."

If we read "spell" for "stone" and apply this understanding of motion to magical penetration, what conclusions can we draw? Is a spell ability to affect a magic resistance target a factor of it's "speed" (in which case the strength of the caster has no bearing) or of the "distance traveled" (in which case it does).

[Marko_Markoko]

But we are not talking speed, we are talking about force and how far a thing travels. Try reading it like this...

"Spells cast by a strong magus do not travel faster than those cast by a weak magus, although they can travel further (through parma)..."

You can throw a light stone further and with more foce than a heavy stone, though the heavier stone, if it reached it's target, will cause more damage because of its weight.

[Cuchulainshound]

I've said it before, but "logic" and "common sense" do not mesh well with discussions of "magic". So do yourself a favor and just accept it as a given. How does it work? It works just fine, thanks for asking.

However, everyone is putting the emphasis on the Spell - which is clearly ~not~ what is going on here. The emphasis is on the Casting Total - that is the yardstick of magical power of a mage, not the size of the spell. A mage has a CreoIgnem of 50 - nice. What does she do with it? Does she use that to conjure up something massive, a lumbering mollusk of a spell - or something small and simple and use the rest of the juice to drive that home?

And the answer is, "It depends on the target" - mundane, the first; magical, the second.

In another common game system, a 5th level spell is clearly "more powerful" than a similar 2nd level spell - but that's not Ars Magica. In Ars, a 5th magnitude spell effect is a more powerful manifestation of that Form than a similar 2nd magnitude spell effect, but that does not make it a "more powerful" spell, except against mundane targets. As soon as we move into the realm of Magic Resistance, it's the mage, and the talent (i.e. "Casting Total") behind the spell, that make it powerful or no.