The thaumaturge class quests state that individuals have "aetheric capacity" that enables them to utilize thaumaturgy. In fact, that's one of the plot points of the questline--the lala brother who became an alchemist and ends up doing A Terrible Thing in order to gain higher capacity.
This particular lala's capacity was so low he couldn't cast even the simplest of spells (i.e. even spells with very low MP cost), even if he could learn the method, he wouldn't have the aetheric energy to fuel them.
This suggests that aetheric energy is the Eorzean analogue to "mana" in other fantasy settings.
This particular lala's capacity was so low he couldn't cast even the simplest of spells (i.e. even spells with very low MP cost), even if he could learn the method, he wouldn't have the aetheric energy to fuel them.
This suggests that aetheric energy is the Eorzean analogue to "mana" in other fantasy settings.
attractive enmity device