Alchemical and magical theory hold that the world is made up of 5 distinct elements, bound and controlled by a 6th element.
The 5 primary elements function in two distinct cycles: The generative or consumptive cycle, and the conquering or destructive cycle. Left alone, these elements would interact rapidly through both cycles; this is prevented, creating a more stable status quo, by the limiting influences of the 6th element.
The element of wood, which also includes plants and growth and is sometimes considered the element of life itself. It is fed by water, and in turn feeds fire; it splits earth, but is in turn felled by metal.
The element of fire. It is fed by wood, and in turn feeds earth; it melts and forges metal, and is quenched by water.
The element of earth. It is produced by fire, and bears metal; it dams and binds water, but is broken up by wood.
The element of metal. It is borne by earth, and begets water by pooling and containing it; metal overcomes wood, but is consumed by fire.
The element of water. It is pooled by metal, and makes wood flourish; it quenches fire, but is dammed by earth.
Aether is the binding and controlling element. Coming from the Otherworld and composing the barriers between that world and this one, aether limits and controls the interactions of the other elements. Magic functions by manipulating, summoning, or dismissing aether in order to allow the other elements to interact more strongly, ideally in a manner controlled by the caster to achieve the desired effect, although oftentimes the effects involve interactions so complex they cannot be readily identified as belonging to one of the elemental interactions.