Humans are peculiar among folk in that they are born with no arcane flavor and no elemental charge. They favor no particular domain. Though they are primarily considered beings of the physical world, they possess an unusual soul that interacts with the unseen world, even without conscious effort or full awareness from the individual.
Because of this neutrality of fettle, humans have no inherent connection to or interaction with the cycle of arcana and therefore have no innate magical ability. However, they have an extraordinary versatility that allows them to learn to wield magic of any domain.
Over time, by interaction with folk and arcana of the cycle, they can shift their fettle toward any of the six domains. This process is usually only possible when undertaken intentionally, but in certain cases of extreme exposure, it can occur inadvertently.
Fettle shifting causes a human to take on physical and magical characteristics of the domain toward which they have shifted. Upon reaching the utmost extreme of shift toward any given flavor, the human will irrevocably become folk of that flavor. Before reaching this point, all changes are ultimately reversible; however, this process is difficult beyond the ordinary means of most if not any individual.