here is an interview from 4gamer with the development team:

"4Gamer: While we are on the subject of character growth, in addition to getting rid of physical levels, you are planning on introducing a job system as well right? Job systems make me think of FFXI but what will it be like in FFXIV?

Gondai: There will be jobs related to each of the classes and you’ll master them by participating in a quest. The jobs aren’t advanced forms of their classes. You’ll be able to choose for yourself whether you want to fight as your original class or as a particular job depending on the situation.

4Gamer: How will things be different if you play just as the class?

Gondai: The jobs are more like a defined style for when you are in a party. When you play as a certain job, the actions you can use from other classes will become limited, but it’ll make your role in the party more defined and you’ll have access to job specific actions.

Yoshida: If you play as a gladiator, you can still use actions from other classes. However, they are still pretty limited in what they can do. So let’s say you switch to a job called “Paladin” (Knight) instead. You can use a sword and shield and you’ll be able to better protect people as a tank.

4Gamer: So if I understand this right, you’ll get access to abilities you can only use as a Paladin?

Yoshida: It’s like you’re wearing an outer shell called Paladin. You could also think of it as a mode change. Of course there would be abilities you could only use as a Paladin. Perhaps for light parties where there are only 4 people, you’ll use various class abilities and actions. However, if you get into a full party where you need some more defined strategy, everybody will switch to a job instead. Narrowing your roles down can help with party balance and make it easier to come up with a battle plan.

4Gamer: So depending on your job choice, you might become a damage dealer or you might become the tank?

Gondai: Right now, it doesn’t work that way. To start, there will be one job per class. As we add jobs in the future, it might be possible to do what you’re thinking though.

4Gamer: For now, we’re just getting one form of specialization per class then. That kind of makes me want to try making battle plans for the new raid content.

Yoshida: Once we’ve finished the adjustments to the battle system, we’ll be able to continue development on content like the raids. I hope people look forward to it."

http://ffxiv.gamerescape.com/2011/06...iew-june-2011/

So i can gather that all "predictions" about jobs that are to come will come true as a "Specializations". i wonder if after you get these jobs you would not be locked to Certain weapons. like a MRD gets a Darknight with job specific ability and then he can use GAXE Scythe GSWORD. i can only imagine