Ars Magica was one of the first magic systems to use what’s now called noun-verb casting, which it expresses in terms of Forms and Techniques. If a spell is a sentence, you express it in Ars Magica using (typically) one Form and one Technique: Rego Animal (ReAn), “I control the animal,” or Intellego Mentem (InMe), “I perceive the mind.”

Arts
  Forms    Techniques 
  Animal (An)    Creo (Cr) 
  Aquam (Aq)    Intellego (In) 
  Auram (Au)    Muto (Mu) 
  Corpus (Co)    Perdo (Pe) 
  Herbam (He)    Rego (Re) 
  Ignem (Ig) 
  Imaginem (Im) 
  Mentem (Me) 
  Terram (Te) 
  Vim (Vi) 


Each of the Arts line up with either a subject or an action. They deal with what kinds of things the spell can affect:


The Techniques describe actions. They deal with what the spell does to the subject:

In addition to the Arts, each Ars Magica spell is expressed in terms of three parameters which define its extents. Each of these parameters has a default at the low end of a spectrum of possibilities. To increase the value of a parameter, the caster increases the magnitude of the spell by an equal number of rows. Magnitude 1 spells below Level 5 are a special case: instead of increasing the Magnitude of the Spell, each parameter shift increases its Level, up to Level 5. After that, shifting a parameter increases the spell’s Magnitude, as normal.

Spell Parameters
  Duration    Range    Target 
  Momentary*    Personal*    Individual / Circle* 
  Concentration / Diameter    Touch / Eye    Part 
  Sun / Ring    Voice / <i>Road    Group / Room 
  Moon / Fire**    Sight    Structure / Bloodline** 
  Year*** / Until**, ***, Year +1**, ***    Arcane Connection    Boundary, *** 
  * - Default Parameter Value. 
  * * - Faerie Magic only. 
  * * * - Requires a Ritual. 


Range
Default: Personal.
The range of a spell is the distance to the nearest part of its target.


Duration
Default: Momentary.
A spell’s duration is the how long its effect remains active. Note that although the effect ends, the effect’s consequences often persist.


Target
Default: Individual.
Target expresses what or how much the spell can affect.


Definitions