《易传·彖传上·恒》
阳刚处上而阴柔处下，雷风相交与，巽顺而动，阳刚与阴柔皆相互应，故为恒。
刚上而柔下，雷风相与，巽而动，刚柔皆应，恒。
The strong and active are on top while the gentle and passive are below, thunder and wind interact with each other, zephyrs blow softly, the strong and active and the gentle and passive respond to each other, therefore it is for constancy. 