Originally Posted by
HeatherRae
To understand how this works, remember that every character can be every Class and Job if they want to take the time to level them. Classes are determined by what weapon you have equipped. For instance, I rolled as a Conjurer, so when I equip wands or staves, it puts me into that class. Jobs, on the other hand, are like "add this on to make you better." You equip a small piece of gear called a Soul Stone (each job has its own soulstone) that makes you be in that particular Job, but you are still also whatever base class you are. As an example, I play a White Mage. White Mage's base class is Conjurer, so I equip staves or wands with my White Mage Soul Stone. I am a White Mage, but I am still a Conjurer at heart.
Every person starts with a base class. For instance, I started with Conjurer. Conjurers are healers, with a bit of DPS on the side for questing. When I got to level 30, I went and leveled Arcanist on the same character to level 15. Once I had Conjurer to 30 and Arcanist to 15, I was given a quest by my Conjury Guild Master to become a White Mage. Jobs level with your Class (they're tied to that class, so when leveling as a White Mage, any XP I receive is Conjurer XP, as that is the base class).
Just like in D&D, to qualify for a Job, you have to meet certain requirements. In FFXIV, this means you need the base class for that Job leveled to 30, and the secondary class leveled to 15. Also like D&D, a Job is more of a "specialized version of this base class." So in the same manner that Archmage is a specialized version of Mage in D&D, Black Mage is a specialized version of Thaumaturge. The most obvious situation with this is the one class that has two Jobs attached to it - Arcanist. If an Arcanist (which is a pet class) chooses to level Conjurer to 15, they can take the Scholar Job, which is a specialized healing role with a pet. If they choose to level Thaumaturge to 15, they can take on the Summoner Job, which is a specialized DPS role with a pet.
This may not have been the clearest explanation, but I hope it helps.