The Job system in Final Fantasy Tactics Advance is a change from most other RPGs, they allow the character to alter the abilities and strengths of any playable character. Each job has either three specific alterations, either more strength-based for example the Paladin, magic-based which could be the Black Mage, or in-between which could be seen as the Morpher job. Each Jobset can be changed at any point in time, and each ability you learn from the job can be used in your current jobset, so if your character, Marche was a Black Mage, and he learned Paladin abilities, then you could still use the Paladin abilites when in the Black Mage jobset. In total, there are Two Command slots in which any Allied Unit can use. The First Ability slot is the current Jobset ability, while the second is the can be selected from the list of Jobset abilites that you have learned.

Final Fantasy Tactics Advance Jobset Requirements
Humans
Job Name	Required A-Abilites
Soldier	N/A
Paladin	2 Solider
Fighter	2 Solider
Archer	N/A
Hunter	2 Archer
Thief	N/A
Ninja	2 Thief
White Mage	N/A
Black Mage	N/A
Illusionist	3 White Mage, 5 Black Mage
Blue Mage	1 White Mage, 1 Black Mage
Bangas
Job Name	Required A-Abilites
Warrior	N/A
Dragoon	2 Warrior
Defender	2 Warrior
Gladitior	2 Warrior
White Monk	N/A
Templar	2 White Monk
Bishop	2 White Monk
Moogles
Job Name	Required A-Abilites
Animist	N/A
Mog Knght	1 Animist
Gunner	1 Animist
Theif	N/A
Juggler	2 Thief
Gadgeteer	2 Thief
Black Mage	N/A
Time Mage	5 Black Mage
Nu Mou
Job Name	Required A-Abilites
Beastmaster	N/A
Morpher	5 Beastmaster
Black Mage	N/A
White Mage	N/A
Time Mage	5 Black Mage
Alchemist	3 White Mage, 5 Black Mage
Illusionist	3 White Mage, 5 Black Mage
Sage	3 White Mage, 2 Beastmaster
Viera
Job Name	Required A-Abilites
Fencer	N/A
Red Mage	1 Fencer
Archer	N/A
Sniper	2 Archer
White Mage	N/A
Elementlist	1 White Mage, 1 Fencer
Summoner	2 White Mage, 2 Elementalist
Assassian	2 Elementalist, 1 Sniper