A comparative study of sheng niu si deng and the classification of 36 letters in SPE feature system reveals that sheng niu si deng is a mature classification based on the feature-differentiation theory.

• 通过声纽四等和SPE特征系统对三十六字母在发音方法分类方面的对比研究，可以看出声纽四等是较为成熟的、根据区别特征原理所作的分类。