Characteristics

Intelligence
represents both your memory as well as your ability to learn and think. It is important for Abilities that require thought power and is paramount for the magical Arts. A character is not necessarily stupid if she has a low Intelligence; common sense, street savvy, and wisdom are not part of the Intelligence score-these are facets of the character that are portrayed by the player.
Perception
indicates how well you notice things going on around you, as well as your powers of intuition. While sometimes a conscious thing, Perception often works intuitively-you simply notice something. Besides letting you notice things, a storyguide may have you roll Perception with various knowledge abilities to see if you have the insight to understand or know about a certain fact or concept. Perception is important for Abilities such as Alertness, Track, and Folk Ken.
Strength
is a measure of your physical power. It is your lifting, pushing, shoving, heaving, and moving ability. Strength is important when hefting a melee weapon, and when using brute, physical force against something or someone. People with higher Strength are often bigger than those with lower Strength, assuming they are within the same Size category.
Stamina
indicates how long you can continue to exert yourself as well as how much physical punishment you can sustain. It is your staying power, both mental and physical, and one of its most important components is simply will to live. Some people are too mean to die. Stamina also helps determine how well you carry a load, ignore fatigue, and withstand wounds.
Presence
describes your appearance, demeanor, and charisma. Personal tastes vary, but within a culture good looks are standard enough that what is attractive, interesting, or impressive to one person is likely the same to others. Presence is also indicative of how imposing or intimidating you are; you might not be physically attractive but your demeanor might command respect. Presence is important for making a good impression, as well as for leading people.
Communication
represents your aptitude for self-expression. It is important when you are attempting to verbally influence or communicate with another, or when trying to do so through body language. Communication is the basis of most human interactions, and a positive Communication score suggests a character who is comfortable with or confident in his relationships with other people.
Dexterity
indicates the physical ability to move with agility and to manipulate what you are holding with accuracy and grace. It indluces hand-eye coordination, fine motor manipulation, and bodily grace. Dexterity helps determine how well you swing a sword or throw a knife.
Quickness
indicates your reaction speed and reflexes. It is simply how fast you are. Quickness helps determine who acts first when two people are trying to do something with great haste. It also determines how well you do something when you do it rapidly. Whenever Quickness modifies a roll, Encumbrance, the measure of how loaded down you are, is applied as a penalty. In other words, you react more slowly when carrying a heavy load.

These descriptions were taken verbatim from the Ars Magica 3d ed. rules. Typos are mine.

Ability conversions for an existing game:
AD&DArs Magica
1-7
2-6
3-5
4-4
5-3
6-2
7-1
8-1
90
100
110
120
131
141
152
163
174
185
196
207
218
229
2310
2411
2512

woodelfwritings
created by woodelf@yar.cs.wisc.edu