To note.
Conjury is the art of speaking with the elementals and drawing the power of the land to power your magic.
Thaumaturgy is the art of using one's own inner aether to perform your magic.
Friend up there said black mages call upon the aether of the atmosphere to power their magic.
A certain conjurer that was... Unwilling to learn. Used her own natural energy reserves to power her healing magic, nearly leading her to death (also the cause of her mother's death).
She was definitely healing with thaumaturgy (which made a friend of mine flip his pancakes, because he played in the earliest stages of the game in 1.0 back when THM was a healer and CNJ a nuker).

Thaumaturgy and Conjury aren't that different at all, they are very alike.

Also, the use of one's aether to power himself is not unique only to magical classes! A certain disciple of war, Monk, uses the power of their own inner aether to strengthen their bodies.