In Zen swordsmanship there are the words hen and sho. Hen means "being partial with a thing." When the mind is directed to a part of the body it is partial or one-sided. On the other hand when the mind fills up the whole body it is said to be sho, meaning "right" or "truth." The right-mind is spread all over the body and is not at all partial or identified. The partial-mind is one-sided, attached to a thing. Zen dislikes prejudice and one-sidedness. We also disregard absorption in all things, because this means identification with something and becomes partial (hen). If there is no thought about where to direct the mind it will be everywhere. Instead of keeping and guarding it as though it were a cat tied to a lead, if you leave it to itself and let it move about it will never go out of your body. Strive (kufu) not to keep it in one place, not to localize or partialize it. Make the whole body the mind. Only by unflagging striving can one attain this. When the mind seems to be nowhere it is everywhere.
When there is some thought in the mind you cannot hear what someone says even though you hear the sound, because your mind is engrossed in what you are thinking. You cannot hear what you should hear, and you cannot see what you should see. Nothing registers in your mind. When you let it go it will become mushin (no-mind) and you can hear and see what it necessary. However, when you think to remove the thought, that very same thought becomes an obstacle in your mind. If you do not think anything at all, then everything in the mind disappears by itself and you will be in a state of mushin. It will take time to be able to empty the mind. If you are always trying to let go of a thought your mind will eventually reach the state of mushin.
(Translated by Nobuko Hirose)