Abilities in Final Fantasy Tactics Advance are in four categories: action abilities, reaction abilities, support abilities, and combo abilities.
Abilities are taught by equipment; action abilities are only learned from weapons, while weapons, hats, shields and armor teach a unit an R- or S- ability. While the equipment which provides the ability is equipped, a unit "masters" an ability by gaining enough Ability Points. If their equipment is changed before this occurs, their AP will remain where it was for that ability. Mastered abilities may be used at any time.
List of abilities
Action abilities are actively used, often special attacks such as magic. They are equipped in sets belonging to a job, two of which may be used at once.
Reaction abilities are used when certain conditions are met after a unit is attacked and often being variants of Counterattack or SOS abilities.
Support abilities are generally in use at all times, and usually enhance other capabilities, or else have effects such as wielding a two-handed weapon in one hand, or using two weapons.
Combo abilities allow party members to initiate or join in on a combo. Combos are usable once the character has at least one Judge Point.