Up until about 1900, it was highly fashionable in Okinawa to have anything or to do anything associated with the Chinese. Thus the character commonly used for Kara in Karate meant "Tang" and referred to the Tang dynasty of China. Later, around 1935, Funakoshi Gichin made a courageous and revolutionary step, he first suggested in newspaper articles and later in his book, Karate-Do Kyohan, that Karate-Do had in fact become a pure Japanese martial art. In an effort to correct the interpretation of Karate-Do as a Chinese art and at the same time to more clearly indicate the nature of the art as a way of life, Funakoshi changed the character for Kara from Tang to Ku. Ku is also pronounced Kara, and is found in the Hanya Shingyo, a Buddhist sutra containing the phrase, Shiki soku ze ku, ku soku ze shiki. In this phrase the essence of Karate-Do is contained. Literally it means, "Form becomes emptiness, emptiness becomes form".

             Shiki is the visible physical form of things. It is the outward appearance of anything, such as a technique or a kata.

Ku is a term similar to the mu in Mushin, and it means “emptiness”. But mu is a specific term relating to the thinking processes of the mind, while ku refers more generally to the state of being, without any regard to form. Ku acknowledges existence, but describes an absence of form in that existence.

Ku is difficult to describe, but easy to feel. For example, in our daily routine, there is a larger process occurring all around us which we never examine, but which we notice and accept. That larger process is the change of seasons. As spring turns to summer, the weather becomes warmer, and one day we notice that it is uncomfortably hot outside. As summer turns to fall and then winter, we become aware of the changes in temperature, and suddenly we realize that it is cold. This change from season to season is ku; the seasons and the changes exist, but they do not rely on conscious action, and has no actually visible form or shiki.

In Karate-Do, the meaning of Kara (Ku) is the same. For example, when a student first learns kata, he must concentrate on the movements, involving him completely in conscious attention to every detail. A great deal of conscious thought is required, and complete attention must be given to shiki, the physical form of the kata. After many repetitions, however, the student does not consciously think so much about physical nature of the movements; they become more natural, and the body remembers the sequence. The form, shiki, is becoming emptiness, ku. Shiki soku ze ku.

After thousands of repetitions (Funakoshi believed that at least three years of solid practice was necessary to master a kata), the kata becomes part of the nature of the student. When we watch a master perform a kata, we sometimes feel that he is moving in another plane of existence. He is no longer doing the kata; the kata is “doing itself” on his body.

No conscious thought is given to the physical form of the kata. The complete emptiness ku is the same emptiness involved in change of the seasons. No conscious thought is involved, and the shiki (the different season or the techniques of the kata) is expressed through his emptiness. Ku soku ze shiki.

In the kata Kanku Dai, the first movements are visual representations of shiki soku ze ku, ku soku ze shiki. The hands move together and rise above the head to look at the sky, and then break apart, moving in wide arc to come back together again in front of the center of the body. Together they are form; apart they are emptiness. Then they come back together.

Form becomes emptiness, emptiness becomes form.