A Brief Primer of the Ars Magica Magic System

The Ars Magica system shines in a couple of areas, but the magic system is widely regarded as the best in the industry. This is perhaps because the system is at once flexible and easy to grasp.

The basic die roll in the game is an open-ended d10 and the basic formula for determining what you can do with magic is

Casting total = die + Stamina score + Form + Technique

'Technique' and 'Form' translate roughly into 'Verb' and 'Object' in a kind of statement. This makes for a pretty intuitive system for determining what you're trying to do. The only downside for newcomers is that the game uses Latin for these terms for flavor...

So someone who wants to hurl fireballs wants to have pretty good scores in Creo and Ignem, while someone who wants to remove a memory from someone favors Perdo and Mentem. There are guidelines for any of the combinations above: hurling a big fireball requires a spell casting total of at least 25 if you know the spell (35 if you don't want to be fatigued) while removing five minutes of a person's memory takes a 0 or 10. (You can make up spells on the fly, but the totals are halved, and you must hit that upper number! So not knowing a fireball spell means you need to total 70 to pull one off!) There's a little more to it than that, but not much.

The spells you know are called Formulaic spells, and you must either roll their level or above to cast them without tiring. If you come within 10 of the level, you lose a Fatigue level, but the spell goes off. Below 10, and the spell fizzles and you lose a Fatigue level. You can cast spells all day, but it takes time to recover these levels, so wizards can quickly tire themselves out—this keeps them from being unbalancing.

Other spells that you make up are Spontaneous, and the most common way to cast them is to halve your casting total. You still lose a Fatigue level, even if the spell works! So what usually happens is you try to duplicate a spell of say, 20th level, but your die total is a 34. For spontaneous magic, that means you pulled off a 17th level spell—not quite what you wanted. You still did something, though, and the GM decides what by comparing your level effect with the guidelines mentioned above.

Exempla gratia: The young magus Cynric Ex Miscellanea wants to cast the spell Lungs of the Fish, which lets him breathe under water. The spell is a level 20 Muto Aquam spell. Rolling a 7 on his die roll, Patrick gets a 26 total (7 die roll + 2 Stamina + 7 Muto + 10 Aquam), so Cynric's spell goes off, and he doesn't lose a Fatigue level—IF he knows the spell. If he were trying to duplicate its effects without knowing it, his total is halved, to 13. An 13th level spell isn't quite good enough, so the Storyguide may decide that he can breathe under water...but not as long as the spell normally allows.