Board Thread:Speculation House/@comment-27276671-20160214220907/@comment-25396609-20160714214417

I think there might be some literal sense to it; but rather than it being some dark force that allows you to draw and control grimm, it may be a balance between the two known aspects of aura.

The light would be the active decisions we make to follow our own path, focusing on the light would be focusing on your semblance. Focusing on and developing those powers unique to yourself.

The dark would be allowing your own unique abilities fall behind while concentrating on manipulating the inherent, generic properties shared by all who wield aura; things like the shields used by Ren and Cinder, or the slash waves used by Blake.

Grimm are anonymous, and as such all grimm have the same powers based on their species; boarbatusks can sonic roll, Nevermore can shoot feathers, etc. The lack of light, or individuality, means they have no abilities unique to themselves.