"Mao Zedong Thought Is the Sole Criterion of Truth"
Source: Translation of "Gei Shoudu dazhuan yuanxiao hongweibing geming zaofan zongbu de xin" (Letter to Capital University Red Guard Revolutionary Rebel Headquarters) in Chinese Studies in Philosophy, Vol. 25, No. 2, Winter 1993-94, pp.15-16.
Students and fighters of the Revolutionary Rebel Headquarters of Red Guards in the Capital's Institutions of Higher Education:
Yesterday I gave a speech at a Red Guard mass rally organized by your headquarters in which I made one rather incomplete remark.1 I now correct and complement that remark of mine as follows:
Immediately after "which you consider to be correct, and consider to be the truth, you may adhere to for some time," it should say "If in discussions or in practice, if you yourselves or someone else has proven that indeed they are wrong or partially wrong, then you should admit your mistakes and rectify them. If it has been proven that indeed they are correct or partially correct, then you should continue to adhere to those words or actions which are correct." This is, as Chairman Mao often teaches us, the principle of "adhering to the truth while rectifying one's mistakes." In the course of this Great Proletarian Cultural Revolution of ours there can be only one criterion of truth, and that is to measure everything against Mao Zedong Thought. Whatever accords with Mao Zedong Thought is right, while that which does not accord with Mao Zedong Thought is wrong. This is why Comrade Lin Biao tells us to "read Chairman Mao's works, obey Chairman Mao's words, and act according to Chairman Mao's instructions." This is something you must bear in mind constantly.
It is my hope that you shall be able to pass on these words to the Red Guards and revolutionary teachers and students.
Great Proletarian Cultural Revolutionary greetings,
27 September