The One Divides into Two controversy was an ideological debate about the nature of contradiction that took place in China in 1964. The concept originated in Lenin's Philosophical Notebooks and was often repeated as part of Mao Zedong's interpretation of dialectical materialism. The philosopher Yang Xianzhen originated the idea of "Two Unites into One", which he said was the primary law of dialectics. The Maoists interpreted this to mean that capitalism could be united with socialism, or that contradictory, inherently antagonistic forces could be harmonious: in both cases Yang was cast as someone condoning reconciliation and capitulation with counter-revolutionary forces and ideas. Ai Siqi wrote the original attack on Yang, and was joined by Mao himself. Wang Ruoshui also contributed to the attack. After 1976, Yang was officially rehabilitated, along with the concept of two uniting into one.