The following is a list of known classes. The first four are automatically attainable, but the others have other prerequisites.

standard classes - all players are provided access to these classes by default.

Fighter
Defender
White Mage
Black Mage

advanced classes - these classes are unlocked by achieving moderate levels in other classes.

Weaponsmaster
Armormaster
Silver Mage
Sorcerer

advanced hybrid classes - these classes are unlocked by achieving moderate levels in multiple other classes.

Red Mage
Sage
Dragoon
Sockmaster

medal classes - these classes are unlocked upon use of a "rare" item.

Blue Mage
Summoner
Scholar
Merchant
Thief