Magic Resistance

Magic Resistance is an ability of characters (and creatures or so on) to remain unaffected by magic. This is very important to magi, who would otherwise be vulnerable to one another's spells and to creatures of the Supernatural Realms.

In Ars Magica Fifth Edition, Magic Resistance works by keeping magic away from the protected target, as detailed in ArM5 page 85. In addition to repelling magic spells, Magic Resistance also stops the malignant social effects of The Gift. The invention of Parma Magica by Bonisagus greatly bolstered the Magic Resistance of magi, which encouraged the formation of the Order.

Magic Resistance is not a Ward. Wards an an alternate means by which wizards can protect themselves from magic.

The Magic Resistance Rules

Magic Resistance has always been one of the most difficult and contentious aspects of the Ars Magica rules. It's simple to understand what happens when someone tries to cast a spell directly on a character or creature with Magic Resistance, but things get tricky as soon as someone tries to affect a character or creature by casting spells on the environment around a character. The interaction of Magic Resistance with various kinds of indirect effects is an abundant source of confusion and disagreement. Many variant rules have been offered over the years.

How Magic Resistance Works

The principle is dead simple: a magical effect can only cross magic resistance if it penetrates. There is a subsidiary principle: magic resistance does not dissociate magical effects from the things they affect. Between them, I am fairly confident that they have the effects described.

--David Chart, Berkeley Ars Magica List, 26 Nov. 2004

Well, I can't really explain much better than the rule book does. The relevant rules are on pp. 85-86; I'll try to rephrase them in case it helps.

First of all, magic resistance works the same way for everyone who has it. In the basic Fifth Edition rules, the only things that have magic resistance are magi (who get it from their Form scores and/or Parma Magica) and supernatural creatures (who get it from their Might score). For convenience, I will write "magus" when I mean "person or creature who has magic resistance," but the rules and the examples also apply to something like a demon, a pixie, or a dragon.

Magic resistance keeps magic away from the magus. It doesn't dispel magic. Page 85 says "[m]agic resistance keeps magic away from the maga, her clothing, and other items that are very close to her." It may help to think of Parma Magica, whose name is Latin for "magic shield," as a force field that surrounds the magus an inch or so outside his clothing. Magic can't get through that force field unless it penetrates the target's resistance. If it somehow does get through - say the magus lowers his Parma Magica and then brings it back up - then the magic is not dispelled. It keeps working.

The key question, then, is what is "magic" for purposes of magic resistance? Just about anything that comes from a spell or magical effect. Magic cannot act across the boundary of magic resistance, so it must penetrate the magus's resistance to affect him directly. Anything created by magic (except by a Creo ritual) would be kept out, as would anything altered by magic. Something propelled by a Rego effect, like Strike of the Angered Branch, would not be kept out, but it would lose all its motive force and come to a complete stop as soon as it hit the magus's resistance. (In the medieval understanding of physics, there was no idea of inertia and things were thought to stop the moment there was no force acting on them.)

The examples on pp. 85-86 explain these ideas in context. Really, the confusion about magic resistance is not usually about how the rules work (that's pretty clear), but about fine points or unpopular implications of the rules.

Who Has Magic Resistance

Humans do not normally have any Magic Resistance. Up through ArM4, everyone had some possibility to avoid or withstand certain magical effects. This was called Natural Resistance. However, Natural Resistance was dropped from the rules in ArM5. Magic now always works automatically unless the subject has Magic Resistance.

Supernatural creatures (of any Realm) always have Magic Resistance. Their Magic Resistance score is usually equal to their Might Score.

The only way humans, including magi, can get Magic Resistance is through a magical effect. Hermetic magi have the best all-around Magic Resistance of any wizards in Mythic Europe, through the Parma Magica. Other magicians (the so-called Hedge Wizards) have either no Magic Resistance at all, or a restricted kind of Magic Resistance that protects against only certain effects. More often, hedge wizards use wards for protection.

Hermetic Magi get their Magic Resistance from two sources: their mastery of the Forms of magic, combined with a special spell-like effect called Parma Magica.

What Magic Resistance Protects Against

Magic Resistance applies against not only magic, but powers emanating from the Faerie, Divine, or Infernal Realm. In short, Magic Resistance provides protection against all supernatural effects. (There is one exception: Magic Resistance cannot protect against a miracle performed personally by God. This is unlikely to happen in a typical Ars Magica game. The actions of other beings with Divine Might, such as angels or saints, are subject to Magic Resistance.)

Non-Hermetic wizards have limited Magic Resistance at best, because they do not know Parma Magica. Their Magic Resistance functions as explained in the description of their powers.

Beneficial Spells

Magic Resistance protects against all spells and effects, including spells the character casts on himself. There is one exception: spells cast at Personal Range bypass Magic Resistance (ArM5, page 85). Such a spell could be cast by the magus personally, or by an effect invested into his Talisman.

Magic Resistance can't tell the difference between a beneficial spell and a harmful one, so it also "protects" against healing spells and the like. Magi can voluntarily suppress their Magic Resistance as noted under "Parma Magica" on ArM5, page 85.

Magic Resistance and Magical Things

Q: How would Magic Resistance affect a sword that's enhanced by a spell?
A: The sword would be kept out entirely unless it penetrated the Magic Resistance.

Magic Resistance keeps out magical things. "Magical things" for purposes of Magic Resistance include anything created by magic, and anything under the influence of an active magical effect.

If someone attacked a magus with a magically-enhanced sword, the sword would be kept out by Magic Resistance. It would have no chance to hit unless it penetrated the magus's Magic Resistance. Since Magic Resistance does not dispel magical effects, it wouldn't keep out "just the magic" and let the blade through to do normal damage.

This is explicitly mentioned in the description of the spell, Edge of the Razor (ArM5, p. 154). The principle comes from the magic resistance rules, not the spell, so it would also apply to effects like Blade of the Virulent Flame even though the spell description doesn't mention it. In the case of Blade of the Virulent Flame, the entire sword would be blocked, not just the flames.

These are the Fifth Edition Magic Resistance rules as written. They are not perfect: there is a well-known flaw commonly known as the Pink Dot loophole.

Magic Resistance and Physical Attacks

Q: Does magic resistance protect against the claws or teeth of a magical creature?
A: Not normally. His claws are not a magical power, most of the time. It's the same reason Parma doesn't stop another magus from punching you on the nose.
--David Chart, Berkeley Ars Magica List, 25 Nov. 2004

The claw of a supernatural beast like a dragon is not inherently magical, any more than the fist of a supernatural person like a magus is magical. Only if the claws or fist were under the influence of a current supernatural effect - something that affects the claws themselves or maybe something that acts through the claws to affect their target - would they be stopped by Magic Resistance.

A related question is whether the attack of a human shapeshifted into an animal could be resisted. Generally speaking, the answer is yes. The shapeshifter is probably under the influence of a current supernatural effect. As noted in Houses of Hermes: Mystery Cults (page 24), a Bjornaer magus in heartbeast form does not count as being under a magical effect.

(One possibility that's just occurred to me, and which apparently didn't occur to the playtesters either -- a magus with a Longevity Ritual is constantly under a mystical effect, so his punches may be affected by Magic Resistance.)
--David Chart, Berkeley Ars Magica List, 25 Nov. 2004

Magic Resistance and Enchanted Devices

Magic Resistance definitely keeps out the effects of enchanted devices - the spell-like magical effects that the devices can create. It is less clear whether magic resistance categorically keeps out enchanted devices themselves (as opposed to their effects). For example, say a wizard has an enchanted staff that can cast a handful of spells. He wants to simply bonk a recalcitrant faerie with the staff without using any of the staff's powers. Can the faerie resist?

On one hand, Magic Resistance keeps out magical things. The staff is magical in some way, since it can produce magical effects. On a simple level, it seems that it would be resisted. If enchanted devices are not kept out, then it seems there may be some kind of evil loophole left open - for example, one could trick a magus into swallowing a small enchanted device, and then activate it from a distance, possibly bypassing the victim's Magic Resistance. The rules do say that enchanting an item is a type of ritual magic (p. 96). It seems that the rules lean toward an interpretation that the staff could be resisted.

On the other hand, common sense says that even if the staff is magic, its magic is not involved in any way when the magus whacks the faerie. The claws of a supernatural beast are not resisted unless the claws themselves are actively magical, so why wouldn't the same principle apply to an enchanted staff? And a rule that the staff would be resisted could make Pentration ambiguous and complicated - if the staff had multiple powers, what Penetration Total would be used if none of those effects were active at the time of the whacking?

There is no official guidance on this question so troupes will have to decide for themselves. It seems to me there are potential complications with either interpretation. I don't want to deal with the Penetration questions that would arise if all enchanted items can be resisted, so I lean toward a ruling that they are only resisted while under some currently-active effect.

--Andrew Gronosky

Magic Resistance and Illusions

Q: Since magic resistance keeps out magical things, doesn't it keep out illusions?
A: Good question. The answer is no.

The Fifth Edition rules did anticipate the interaction between Magic Resistance and illusions. Under the description of the Form of Imaginem on p. 79, the text explains that Imaginem spells produce non-magical species that can't be magically resisted. So, any Imaginem spell looks the same to a person with Magic Resistance as it does to one without it. Incidentally, this rule also prevents the detection of visual illusions at Touch range by simply seeing (touching with your eyes) the species. An illusion-detecting spell would need to target object from which the species originate, not the species themselves.

References

ArM5 p. 85.