The modal system in kangen music
Although the Japanese modal system includes twelve chromatic tones, one of the instruments of the kangen ensemble, the mouth organ (shô), can only produce nine of the twelve chromatic tones. These nine tones form the theoretical and practical basis of the six main Japanese modes.
Nine tones available on the mouth organ (shô)
The Japanese modal system is divided up into three groups of two modes: a Shang-type mode (ryo scale, similar to a Mixolydian mode) and its relative, a Yu-type mode (ritsu scale, similar to an Dorian mode). Using the Western modal denomination, the three modal systems can be described as:
Modal System I: D Mixolydian (Ichikotsu-chô) and A Dorian (Oshiki-chô)
Modal System II: A Mixolydian (Sui-chô) and E Dorian (Hyô-jô)
Modal System III: E Mixolydian (Taishiki-chô ) and B Dorian (Banshiki-chô)
Only the following four pitches are used as fundamental tones: D, A, E, and B, within each of the modes they act as pillar-tones. Figure 2 shows the three modal systems where the pillar-tones are indicated as a half-note.
Japanese modal system
The three most important pitches in each scale are defined as the ‘tonic’, the ‘dominant’, and to a lesser extent the ‘sub-dominant’. Within a mode, these three key-tones are often sustained since they serve as point of arrival and/or rest for most melodic lines. In gagaku music all sustained-tones are ornamented, but the ornamentation of the four fundamental pitches is rhythmically and melodically much subtler than that of the three other tones. Therefore a mode whose tonic, dominant and sub-dominant correspond to fundamental tones is more stable, since its 'resting' tones are subtly ornamented. In fact, the three key-tones of the six basic modes correspond to fundamental tones, except for two modes: Ichikotsu-chô and Banshiki-chô. The ‘sub-dominant’ of the former is G, while the ‘dominant’ of the latter is F#. Hence these two modes are less stable than the other four since one of their key-tones is more heavily ornamented. Some works have circumvented this issue by favoring the use of Ichikotsu-chô’s ‘sub-mediant’ (B) instead of its ‘sub-dominant’, and Banshiki-chô’s ‘mediant’ (D) instead of its ‘dominant’. It should be pointed out though that gaining rhythmic stability comes at the cost of tonal clarity.
The three other tones (Eb, F, and Bb), appear only as transient tones during the production of ornamental figures. Finally, there is a seventh mode that is outside of the common six-mode system system called Sôjô (G mixolydian), it is rarely used because the pipe producing the F natural is no longer available on the contemporary shô.