6 ideas
In Chinese painting the unpainted surface is not background or leftover space but the element that makes the painted forms function. Void is where breath (qi) circulates between forms. Without it the brushed elements would be inert, so leaving silk blank is a deliberate structural act rather than a failure to finish.
Cheng describes a third term, the median void, that sits between the yin-yang poles. It is not merely a gap between opposites. It is the space of interaction that lets each pole draw from and turn into the other. Duality becomes a dynamic triad, and transformation happens only because an open interval exists between the two terms.
The brush (bi) supplies line, structure and bone, while ink (mo) supplies wash, tonal gradation and flesh. A painting succeeds only when the two are balanced, with neither dominating. Each stroke is judged by how it joins articulate form to diffuse atmosphere, which in turn opens onto the void around it.
Clouds and mist are the void-element that converts one into the other. Seen this way, a landscape is a diagram of how the universe breathes rather than a view of a place.
Blank areas are places the viewer's imagination and breath can inhabit and complete. The painting therefore stays open and continues generating meaning after the brush stops.
Qi is the animating breath that runs through the cosmos, the painter's body, the brushstroke and the finished work alike. The first canon, 'breath-resonance, life-movement,' makes transmitting this rhythmic vitality the highest criterion of a painting. The void is the channel qi needs, so resemblance counts for less than whether breath circulates.