Shinros is correct about Conjurers and White Mages. White Magic also draws more on the world's own Aether supply. Because of this, irresponsible overuse of White Magic resulted in an Umbral Era. You are, perhaps, aware that we are defeating The Primals because they utilize the worlds Aether? The Umbral Era caused by White Magic overuse is similar to the Aether overuse caused by the summoning and maintaining of a Primal. When the Umbral Era occurred, the practice of White Magic fell out of use and was lost to the common person. The Padjal of Gridania became the keepers of this forbidden knowledge and restricted its teaching and use to other Padjal. To learn more about why adventurers can become White Mages, go level one yourself. =P

In short, the only thing that Conjury and White Magic has in common with the other disciples of magic is that it uses or is supplemented by Aether.