The Song philosopher Zhang Zai wrote in Correcting Youthful Ignorance (正蒙): “Where there are images, there are pairs. Each pair acts in opposition. Where there is opposition, there is enmity. Enmity must be resolved through harmony.” In the original, the last line is 仇必和而解.
The philosopher Feng Youlan quoted these four lines in the conclusion of his New History of Chinese Philosophy. Marxist dialectics, he wrote, would accept the first three. “But Marxism would not say the fourth… My guess is that it might say: ‘enmity must be fought to the end.'”