《黄帝四经·十大经·观》
阴阳聚合，刚柔相济；刚柔的相辅相成，阴阳的融会贯通，便成就了万物。
牝牡相求，会刚与柔。柔刚相成，牝牡若形。
Yin and yang come together, and rigidity and softness complement each other; the combination of rigidity and softness and the fusion of yin and yang contribute to all things.