The debate about whether practice is the sole criterion for testing truth was a nationwide movement that took place before the convocation of the Third Plenary Session of the Eleventh Central Committee of the Communist Party in December 1978. It was designed to educate the people in Marxism and to emancipate their minds. After the downfall of the Gang of Four, the Party Chairman, Hua Guofeng, who was in charge of the work of the Central Committee, clung to the erroneous notion of the "two whatevers" (see note 9) and reaffirmed the wrong theories, policies and slogans of the "cultural revolution". On April 10, 1977, Deng Xiaoping wrote a letter to the Central Committee, proposing that to guide the work of the Party, it should use instead a correct understanding of Mao Zedong Thought as an integral whole. Later, he talked with Party comrades on many occasions, explaining to them that the "two whatevers" did not accord with Marxism.

On September 19, 1977, when talking with the leading member of the Ministry of Education, Deng said that seeking truth from facts was the quintessence of the philosophical thinking of Mao Zedong. On May 11, 1978, Guangming Ribao (Guangming Daily) carried an article entitled "Practice is the Sole Criterion for Testing Truth", which stated that the most fundamental principle of Marxism was the integration of theory with practice. This was a criticism of the principle of the "two whatevers". It was this article that gave rise to the debate about the criterion for testing truth. Hua Guofeng and others tried to suppress the debate, but as the majority of the central leaders, including Deng Xiaoping, were fully in favour of it and took the lead in it, it gradually spread throughout the country. The debate demolished the "Left" ideology that had long shackled people's minds and laid the theoretical and ideological foundation for the convocation of the Third Plenary Session of the Eleventh Central Committee.