While this literally means "lines employed in painting," it is used to refer to the fundamental rules guiding the art of painting and, furthermore, to the universal laws of the formation and development of everything in the universe. This notion was first put forward by the Qing-dynasty painter Shi Tao（1641-1718？）, though his ideas were controversial among contemporary scholars and artists. Shi, drawing inspiration from Daoist philosophy and Chan theory, and perhaps from Fuxi's use of a single line to symbolize yin and yang as a unitary whole in creating the eight trigrams (eight combinations of three whole or broken lines formerly used in divination), held that all things in the universe derive from a single oneness. All tangible things under a painter's brush, likewise, forever have that oneness at their core. For him, oneness means naught. Painting is thus a process of generating tangible objects from nothing. This is also the ultimate dao -- a combination of the way of painting with that of all things in the universe. As well, oneness is a set of broadly applicable rules present throughout the process of painting. Each stroke or line reflects these rules. The oneness in painting theory encompasses multiple relationships between oneness on the one hand, and the dao, nothingness, tangibility, and multiplicity on the other. It is rich in philosophical implication and artistic significance. This term later became an important part of traditional Chinese aesthetic thought and painting theory.

Oneness in painting is the foundation of all things and phenomena in their formation and development. We can perceive it if we are willing to experience it with our soul. It inheres in our souls though we do not quite understand it. (Shi Tao: On the Principle and  Techniques of Painting)

To feel the universal laws of the nature needs to focus on the things at hand. Capture the essence of life and the universe. Oneness in painting is the most basic skill of painting and calligraphy; its numerous variations are a most basic measure, too, for the execution of brush and ink. (Shi Tao: On the Principle and Techniques of Painting)