Ability Modifier is a consolidated form of the former ability boosting mods (heal amount, combat art damage, etc). It's a straight modifier of said ability's effectiveness (so +damage for CAs, +chance for taunt, etc), but also has a cap of 50% of the base amount for that ability (so if a CA does 10 damage, the max Ability Modifier could add is +5).
Did that make any sense? ;)
Edited, Jun 7th 2010 7:44am by Cyliena