Axis system

In music, the axis system is a system of analysis originating in the work of Ernő Lendvai, which he developed in his analysis of the music of Béla Bartók.

The axis system is "concerned with harmonic and tonal substitution", and posits a novel type of functional relationship between tones and chords. Lendvai's analyses aim to show how chords and tones related by the intervals of a minor third and tritone can function as tonal substitutes for one another, and do so in many of Bartók's compositions.