The purpose of this article is to treat, from different points of view, the revolutionary style of Debussy, and to show what place he occupies in the history of modern music. The writer of this aritcle wishes, firstly, to classify the characteristic aspects of Debussy's method of harmony and through his method of harmony, to reveal one of the techniques which enabled him to produce such sensitive and colorful musical effects. Secondly, the writer tries to explain how the classical, traditional theory of cadence had found a way of servival despite the great upheavals which had taken place in the world of modern music. Also how in the modern mothod of harmony, the control of the tune has become of secondary importance, while the principle of the overtone has still functioned. Lastly, the witer wishes, through an examination of the way in which Debussy solves the tune problem in his composition, to define the position of Debussy in the transitional stage between classical and modern music.