"Man is mortal and art is eternal." We find this fine expression in 'Kwakyo' (花鏡), one of Zeami's writings. In this short sentence, the important problems of his lifelong-training-theory are included in a suggestive style. From two points of view, the space and the time, these problems are made inquiries as follows:- A) From the view-point of space, the theory of the 'Utsuwa' (器) is the starting point of his inquiries. 1) The theory of the Two Mediums and the Three Roles (二曲三体), explaining the contents of learning in the Noh drama. 2) The theory of the Master yand the lack of Mastery (有主・無主). 3) The theory of the Skin, Flesh, and Bones (皮肉骨), inquiring the problem of three dimensions or aspects of display. 4) The theory of the Essence and Performance (体用). The essence is a flower, and performance is fragrance. In training of Noh-drama, to resemble the essence is desirable and to imitate the performance is forbidden. B) From the view-point of time, the logic of the 'Nine Stages in Order' (九位) is the basis of the following theories. 1) The theory of the Owlet (流離の子=梟の雛), inquiring the problems of suitable tearing in each stages in order. 2) The theory of the Seedling, Ear, and Corns (苗秀実), being the analogy of growth of the rice plant. 3) The theory of Never-forget-original-intention (初心不可忘), studying the problem of succession of art from generation to generation.