Japanese people in ancient or middle times, unable to distinguish mind from flesh, sought "mind" (Kokoro) in everything expressed. Regarding "mind" as superior contents of an expressed work, they had a competitive spirit to try to elucidate "mind" within the limit of expressional media. Such a competitive spirit played as a motive power in a creative process. In the course of time, they found "mind" not only very much complicated in meaning, but available to act as a core in a work. According to a principle fromed from long Japanese tradition of poetry, "mind" is a core which unifies all phenomena and which is capable to express maximum meaning by minimum device of expression. This principle was also derived from deep-hearted contemplation or observation on delicate changes or progresses of nature, and it is a theoretical support to some special artistic ideas of Japan, for example "Yugen", "Yojyo", which contain more than expressed meaning. And it formed a back-bone in "Noh", too ; it is the result of competitive spirits of Japanese poets, artists more than sentimentality of the nation.