When the brush moves, water flows from a spring

'Consider that when the brush moves, water flows from a spring, and when the brush stops, a mountain stands firm' -  Sun Guoting (648-703)

Sun Guoting, part of the Treatise on Calligraphy, 687

 
In Tim Ingold's book Lines: a Brief History he quotes two writers on the history of Chinese calligraphy (Yen and Billeter) who describe the importance that has been attached to emulating nature - not in its forms, but in its movements.  Sun Guoting, for example asked his readers to consider the difference between two strokes - the 'suspended needle' and the 'hanging-dewdrop' - and to draw inspiration from rolling thunder, toppling rocks, flying geese, animals in flight, dancing phoenixes, startled snakes, sheer cliffs, crumbling peaks, threatening clouds and cicadas wings.  An earlier Jin Dynasty text, Lady Wei's Chart of Brush Manoeuvres (quoted by Yen, but not by Ingold), suggests that 'an elongated horizontal line should convey the openness of an array of clouds stretching for a thousand miles' whilst a dot should 'contain the energy of a rock from a mountain peak.'  A sweeping stroke (na) should contain the 'orgiastic vigour of rolling waves, or crushing thunder and lightning.'

From Billeter's The Art of Chinese Writing Ingold gives five more examples:

• A thirteenth-century master who compared the moment the brush makes contact with the paper to ‘the hare leaping and the hawk swooping down on its prey’
• Another who in writing two particular characters tried to move his hand like a flying bird, and for two others imitated the 'somersaulting of rats at play'
• The Sung Dynasty calligrapher Lei Chien-fu who 'described how he heard a waterfall, and imagined the water swirling, rushing and tumbling into the abyss. ‘I got up to write’, he recalled, ‘and all that I had imagined appeared beneath my brush''
• Another Sung Dynasty calligrapher, Huang T’ing-chien (Huang Tingjian, 1045–1105), who only mastered a particular stroke after observing the way boatmen on the Yangtze River angled their oars 'as they entered the water, pulled through in the development of the stroke, and lifted them out at the end, and how they put their whole body into the work'.
• And a treatise on painting from the same period describing the way Wang Hsi-chih (or Wang Xizhi, 321-79) drew inspiration from geese, whose necks undulate like the wrist of the calligrapher

 Qian Xuan, Painting of Wang Xizhi (and geese), thirteenth century.