One of the players in the saga I'm running has the Magic Addiction Flaw, and wants to enchant an item with am effect to boost the Concentration roll he has to make to stop casting spells. We looked around the guidelines, and decided that magic can't really provide bonuses to abilities per se, but that it often can provide "indirect" bonuses to some uses of abilites, like the Rego Corpus Gift of the Bear's Fortitude spell which provides a +3 bonus to Soak.
In our saga we have approved a Muto Corpus spell called Eyes of the Eagle that gives a similar bonus to good eyesight, based on the same general concept of the Muto Corpus Eyes of the Cat but with a base of 10 for a +2 to rolls involving eyesight and adding an Animal Requisite. So we thought a similar spell could be created for Mentem that gave a small bonus for the specific task of calming down your addiction-fueled obsession long enough to stop casting spells.
But when looking around the Mentem guidelines, we found several candidate for helping someone break out of an "addicted mindset" and stop abusing some substance (magic in this case). The Perdo Mentem level 5 guideline "Quell an emotion in a person" seems like a good candidate, as does the Rego Mentem level 10 guideline "Control an unnatural emotion (for example, cultivate a person’s feelings of bravery where he is usually cowardly)" in the sense of cultivating a calmer emotion that was not natural to him, as in the example. But the Creo Mentem level 10 guideline "Spark a twinge of conscience in an intelligent being’s mind, overriding the temporary obsession of a demon" from Art & Academe page 35 also seems like it could be adapted to override the addiction's obsession, as does the Muto Mentem level 4 guideline "Completely change a person’s emotions" if you think the obsessive mindest is an emotion, or the Rego Mentem level 4 guideline "Control a target’s mental state (for example, awake, asleep, or confused)" if you think the obsessive mindset is a mental state.
So my question would be, with so many different guidelines that seem like they might apply, but no clear winner, which one do you think would best suit the task?
For easier reference, I've collected below the guidelines I mentioned above:
Creo Mentem 10 - Spark a twinge of conscience in an intelligent being’s mind, overriding the temporary obsession of a demon (Art & Academe 35)
Muto Mentem 4 - Completely change a person’s emotions
Perdo Mentem 5 - Quell an emotion in a person
Rego Mentem 4 - Control a target’s mental state (for example, awake, asleep, or confused)
Rego Mentem 10 - Control an unnatural emotion (for example, cultivate a person’s feelings of bravery where he is usually cowardly)
Covenants p.122 box Example Laboratory Spells has The Resolute Mind of the Tireless Researcher: "The target of the spell finds his mind resolutely fixed on the task in hand, and does not waver from it." Some arguments about this spell's long time consequences follow in its description.
In general, concentrating to stop casting spells will interfer with concentrating to maintain spells, won't it?
More trickily: casting a spell to boost Concentration on not casting spells feeds the Magic Addiction, and gives a +3 for further Int+Concentration rolls immediately afterwards anyway.
Obviously, which is why he was thinking about enchanting the effect on an item instead of casting the spell himself. Also, he's a Verditius, so that's kind of the natural route for him to follow.
Nice catch! Seems like a nice base from which to work. Though maybe it should be Perdo Mentem in this case, since what he wants is to "break focus" from continuously casting spells.
Look up Singlemindedness of the Concentration Wizard (A&A p. 34). Sounds like what you're looking for. That being said, in ars magica, there's usually more than one way to kill a bird. You listed different guidelines, and more than one of those could be a starting point to create an effect, but they likely would work in different manners. Overall, I agree with your conclusion: no one guidelines boosts a given skill, the boost to a given skill is a side-effect of something else. So the first step, if you were to create a new spell, would be to identify what kind of effect you are actually creating, and why that effect has an impact on concentration, on the addiction, etc. But if you're just looking to boost concentration, the above spell will work and save you a lot of thinking.
As a side note, and after talking with the player that wanted this, he's thinking about a Perdo Mentem effect that affects the imagination (as per A&A page 33), to make him stop thinking about magic. Instilled into a talisman with Personal range and automaticall triggered by another, Intellego Mentem effect that he has still to think about.
In case anybody finds it interesting, here's the effect he thought up:
The thought of magic vanished Perdo Mentem 10 R: Personal, D: Momentary, O: Individual
All images of magic are removed from the imagination of the target, who immediately stops thinking about magic. If he suffers from a Magic Addiction Flaw, this addiction will immediately fill his imagination again with images of magic, but the brief respite provided by the spell will give him a +2 bonus to his Intelligence + Concentration roll. If he suffers no such addiction, or suffers from it but resists it with a successful Concentration roll, he cannot cast any more spells for the remainder of the round. (Base 10)