From Vanguard Wiki
The Adventuring Sphere is probably the most synonymous with MMORPG gameplay. Adventurers will explore the world of Telon, combatting dangerous creatures, carrying out epic quests, obtaining excellent loot and protecting people and places from attack.
Called a character's “adventure class” in Vanguard--i.e. the adventure sphere class of the character--it would be known in earlier RPGs simply as character class. Adventure classes include such RPG staples as warriors, clerics, and rogues.
Sigil has categorized adventure classes based on the role each class will play in a group. Sigil identifies these roles as "jobs." There are four jobs: protective fighter, offensive fighter, healer, and arcane caster. There are various classes that can perform those jobs; for instance, the Warrior and the Paladin are both protective fighters, so if a group needed a tank, they could fill that need with either the Warrior or the Paladin.
The job system led to fears from some parts of the Vanguard community that the classes would be bland and indistinct based on past experience with games that used an archetype system. This appears not to be the case. Unlike some other games, Vanguard's classes are unique from the get-go - in other words, you do not start off as a generic "fighter" class and then subclass from there; you simply choose your class and play it. Because the classes within a job are not starting from the same place, there is no necessary overlap in skills. Sigil is committed to making each class unique and distinct from the other classes, even those that perform the same job. For example, both the Sorcerer and the Necromancer are currently listed as classes that can handle the arcane caster job, but the Sorcerer does it through harnessing the power of the elements to cast his spells, while the Necromancer will likely depend heavily on his pets. Both get the job done, but a player would have a much different experience getting the job done with the Sorcerer as opposed to doing it with the Necromancer.
Shortly after E3, Sigil CEO Brad McQuaid was kind enough to throw some red meat to the Vanbois in the form of a tentative list of classes, with the explicit caveat that the list is not final and may be subject to significant revision.