As Western music advanced from the stage at which it was based on musical modes to the stage at which it was based more on tonality, the theory of equal temperament, which was suitable for modulation, was introduced and superceded pure temperament.
西洋音楽は、その発達の段階で旋法から調性音楽に基づくようになり、純正律に代えて転調に有利な平均律を導入してきた。