"Mu" meaning negation, "Shin" meaning heart, mind, feeling. Often translated (confusingly) as "no mind." A Zen term referring to that state of mental clarity and enhanced perception (sensory and intuitive) known as pure mind, produced by the absence of conscious thought, ideas, judgments, emotion (fear and anxiety), pre-conception, or self-consciousness.
A product of Zen meditative training. For the warrior, meditation (towards mushin) was an important compliment to technical training. Through mushin the mind is not absent, but instead is freed. No longer inhibited, slowed, distracted, or clogged the mind was free to fully perceive, respond and commit to action. The mind is not fixed on anything and is open to everything; a mind expanded through the whole body with total awareness of and focus on everything.
The concept was developed by Hui-Neng (Wei lang in Chinese), the sixth Patriarch, or successor to Bodhidharma, who brought to China (and the Shaolin Monastery from India) meditative Buddhism and the concept that all the world comes from the mind and meditation should be used to attain a state of pure mind without stain or dust.
The concept is closely akin to the Taoist concept of stillness (inside) within motion. Lao-Tsu said "The stillness within stillness is not the true stillness (as in meditation), the true stillness is within motion." A term closely akin to Fudo and Fudoshin.
or......to put it another way...
When performing, practicing or using karate, one must maintain a "mind like water". This refers to the mental attitude while facing an actual opponent. It refers to the need of making the mind calm, like that of an undisturbed body of water.
Smooth water reflects accurately the image of all objects within its range, and if the mind is kept calm, comprehension of the opponents movements, both psychological and physical, will be both immediate and accurate, and one's responses, both defensive and offensive, will be appropriate and adequate.
On the other hand, if the surface of the water is disturbed, the images it reflects will be distorted. In other words, if the mind is preoccupied with thoughts of attack and defence it will not properly comprehend the opponent's intentions creating an opportunity for the opponent to attack.
Water also has other properties. Water can be quite destructive. In fact, over time, water is one of the most destructive forces on earth. Your mind must be like water. When necessary, be as destructive as you must.
