Aristotle, chains of causes, cooking and archery

The recent discussion about whether magical Ignem can make items non-magically hot (and magical Aquam make them non-magically drenched!) made me think about a few more issues with Ars Magica's "Aristotelian" physics; in particular, with the physics of a moving projectile.

According to Aristotle, an external force needs to be constantly acting on an object to keep it moving, unless it's going in its "natural direction" (e.g. a bubble of air rising upwards in water, or a stone falling downwards). For projectiles, which clearly keep moving after they have been thrown, Aristotle claims it's the displaced AIR that keeps propelling them. Now, if you throw a mundane projectile with a magically created sling or other initial "mover", the mover (magically) propels the projectile, which then moves the air, which propels the projectile further etc. - until the projectile, propelled by the air it keeps displacing, strikes its target. Why does parma stop the projectile? After all, the magical sling is no longer acting on it after the initial throw. It's the air that is pushing the projectile after that, and in particular the last few inches into the parma.

Now, you can argue that Aristotle saw the nature of a chain of causes as residing in, and partaking of the nature of, the initial cause (e.g. a tree can generate another tree through a seed, because the seed carries the "treeness" property of the initial tree even if it is not a tree itself). This would explain why the projectile stops: the "motion" originates in magic, and partakes of its nature all the way to the end, even if the intermediaries (the projectile and all the atoms of air that are first displaced by the projectile and then propel it forward, causing it to displace more air etc.) are non-magical and not directly affected by magic.

But if we reason this way then, when you a make a container (say, a cooking pot) magically hot, that container should not be able to remain hot after the spell ends, and it should not be able to make its contents (say some soup) non-magically hot (and thus unresisted by parma). Because ultimately, the initial cause of the container and contents' heat lies in the magical Ignem, and so the heat should share the same fate as the spell. But this appears to contradict the current examples of Creo Ignem!

Any way out of this conundrum?

A Rego spell which uses a sudden impulse to launch a projectile does NOT need to penetrate Parma Magica, but does require a Finesse roll to aim since it does not have magic to guide it to its target. Spells like Invisible Sling have to penetrate because the magic moves the object in a manner resembling telekinesis. Thus when the motive force is terminated by the Parma Magica, natural motion takes over.

I hope this post helps, I'm having some trouble explaining it clearly though. HoH: S, now sadly out-of-print, did a good job explaining how such spells work though.

As for the water question, I'm not really sure. I'm afraid, all I know about Aristotlean Physics is what I've learned from Ars Magica over the years... :blush:

Ah, interesting! This clears up a lot of things.



Guess why we play "real" physics(+)? And we dont even know if anyone truly believed in Aristotelean phsyics or if it was just another of those "ah, but this is philosophy! it doesnt need to make sense" matters. Like how Chinese philosphers considered the earth flat despite chinese overall at the same time knowing very well that it wasnt.
The reason to always keep any philosophers getting dangerously close away from you with a properly sized pointed stick... :wink:

You can counter with Ward vs thrown missiles - ReAu A barrier that stops the vacuum effect from pushing an item through the air. Would do nothing vs swords, or people walking through it. It would have to be large enough to get to the end of a missile where the vacuum effect occurs. Once the air stopped pushing an object the terram in it would tak over and it would just drop to the ground.

Interesting point. This is discussed in Houses of Hermes: Societates in the Flambeau chapter. Well, the effects are discussed, not the physics. One of the features of those rules is that you can indeed huck a rock with magic and have the magically-hucked rock go through Parma. That is the whole basis of the School of Vilano. I believe Art and Academe goes into more detail about how and why this works.

From an out-of-character point of view, the choice is this: either shoot your projectile and let it be propelled by air displacement (in which case it's Aimed but not resisted) or carry it with magic directly all the way to the target (in which case it's resisted not Aimed).

I must admit I truly hated this idea. It seems such a 'cheap' method of bypassing parma. The fact that it works wthin the idiom thus defined doesn't make me feel any better. Mages are easy targets and this makes Bonisagus' discovery a bit lame for providing a vehicle for mages to gather and share knowledge in safety. It also makes projectile deflecting sun durations spells almost madatory in the sagas I have endured where this is common. Most mages spend their adventuring lives surrounded by mini-hurricanes.

As I have said several times already, Parma is crap at keeping you alive vs other hermetics. What it is good at is because it removes the penalties of the gift, and protects you against supernatural creatures and most non hermetic magi (excluding vitki) quite well. And only that is enough to make it a worthwhile ability


While I doubt I can persuade you to hate the idea less, I have always thought of Parma Magica as just one of the defenses available to magi. The Code of Hermes is another - you shouldn't have to defend yourself against Hermetics on a regular basis. YMMV. Fast-cast spells are a third.

Parma and fast-cast spells are complimentary. Parma blocks the high-magnitude effects that commonly have low Penetration, and fast-casting blocks the low-magnitude effects that commonly have high Penetration. In my opinion (non-canonical) this is why House Diedne was able to put up such a good fight and stand up to all the other Houses for so long. It's also the reason House Flambeau started using dimicatio in tournament, to develop that style of defense for themselves.

From a playability perspective (again in my personal opinion), I think the Magic Resistance rules in general are designed for magus-vs.-creature conflict more so than magus-vs.-magus. If you're facing a big lizard whose Magic Might is too high for you to fricassee with one spell, at least you can throw a rock at it. Without an attack that bypasses Parma, what are your options? The game has to be playable for weak magi as well as mature ones.

Now, if you are playing in a Saga where magus-vs.-magus battles are the rule rather than the exception, then the assumptions that I think are built into the rules don't apply. You should talk to your troupe about how you can change things to work better for the stories you want to tell.