“There are strict, and when once understood, reasonable and helpful laws for the use of the brush (YOHITSU), the use of sumi (YOBOKU) and the use of water-colors (SESSHOKU). These laws reach from what seems merely the mechanics of painting into the highest ethics of Japanese art.

The law of YO HITSU requires a free and skilful handling of the brush, always with strict attention to the stroke, whether dot, line or mass is to be made; the brush must not touch the silk or paper before reflection has determined what the stroke or dot is to express. Neither negligence nor indifference is tolerated.

An artist, be he ever so skilful, is cautioned not to feel entirely satisfied with his use of the brush, as it is never perfect and is always susceptible of improvement. The brush is the handmaid of the artist’s soul and must be responsive to his inspiration. 

The student is warned to be as much on his guard against carelessness when handling the brush as if he were a swordsman standing ready to attack his enemy or to defend his own life; and this is the reason: Everything in art conspires to prevent success. The softness of the brush requires the stroke to be light and rapid and the touch delicate. The brush, when dipped first into the water, may absorb too much or not enough, and the sumi or ink taken on the brush may blot or refuse to spread or flow upon the material, or it may spread in the wrong direction. The Chinese paper (TOSHI) which is employed in ordinary art work may be so affected by the atmosphere as to refuse to respond, and the brush stroke must be regulated accordingly. All such matters have to be considered when the brush is being used, and if the spirit of the artist be not alert, the result is failure.”
– Henry P Bowie: The Laws of Japanese Painting c.1911