Aether may be pulled from sources other than nature and within oneself, as the White/Black Mage dichotomy exists. Astrologians break this mold, pulling Aether from the stars themselves, as do arcanists (from symbols that "enhance" their own Aetheric reserves), Scholars, and Summoners (both use the same basis as arcanists but then also pull from the Aether of the entities summoned as well). Square could even go so far as to make Geomancy a heretical branch of conjury should they choose; there are multiple possible answers to the lore problem for sure.