"The simple aesthetic requirement by which art should picture the inexpressible developed into a highly complex and comprehensive repertory of artistic principles and technical rules. One of the most significant sources for Southern Song poetry criticism, Yan Yu (1180-1235), defined the poetic as follows:
poetry excels by its transparent luminosity.... It is like echo in the air, color in form, the moon reflected in water, or an image in a mirror; words have limits, but the meaning is inexhaustible.A painting that matches this goal does not simply illustrate poems by means of narrative motifs easy to recognize; rather, by its subject matter, composition, and ink technique, it carries an expressive charge beyond its forms so that one can recognize moods and an emotional atmosphere that are of a sympathetic nature as in a poem."
Above quote taken from Dreaming the Southern Song Landscape by Valerie Malenfer Ortiz, page 65 (Brill, 1999).