Ahh, primal theory. You want mine? Cause it's deep. You've been warned.

Primals are described as being amongst the aether, and when summoned out consume it to maintain a corporeal form. They have thought and emotion, with which they temper others to share a belief in them. Primal manifestations are influenced by faith, which is thought.

Hydaelyn, the lifestream of aether in the planet, has also crystalised into a being with thought. One that can hear, feel, think and influences others to do so. The manifestation of Hydaelyn is in many ways like the manifestation of a primal.

Aether is the source of life and life interacts with aether.

To me, this all implies that aether itself can hear, feel and think. And thus it can develop emotions. This power interacts with the thought of the life it flows through. Thought and belief breeds, creating a manifestation of what people believe the world to be like, including all of its magical characteristics and resident gods.

6 elements would thus exist because the world believes they exist and the aspect of each can be crystalised from it. But that is not all that can be crystallized. If something is believed in strongly enough, anything becomes possible.

(I'm not trying to draw any direct comparisons to the Fayth of FFX here, but I won't object to any indirect ones.)

Time will tell how close I am to the mark.