On this day, 73 years ago, on April 1, 1952 (March 7, 1952 in the lunar calendar), Mao Zedong's "On Contradiction" was published. On April 1, 1952, Mao Zedong wrote "On Contradiction" in 1937, published. "On Contradiction" was written after "On Practice" for the same purpose, that is, to overcome the serious dogmatism existing within the party. The article summarizes the struggle between the two world outlooks of materialist dialectics and metaphysics, and inherits, defends and develops Marxist dialectics. This work is Mao Zedong's important contribution to the treasure house of Marxism-Leninism philosophy.