p To find a criterion of truth is to find the objective basis which does not depend on man and makes it possible to distinguish truth, true knowledge, from delusion.

p Practice is the sole criterion of truth. We can argue as much as we like about the true character of any idea or scientific theory, but this dispute can only be settled by practice, i.e., in economic production, political life or scientific experiment. “The question whether objective truth can be attributed to human thinking is not a question of theory but is a practical question,” Marx wrote. “Man must prove the truth, i.e. the reality and power, the this-worldliness of his thinking in practice.”  [169•* 

p Idealists of all kinds disagree with this important proposition of dialectical materialism. They deny the importance of practice in knowledge and maintain that man himself, his thought, is the criterion of truth. What is useful, what is beneficial is true—this idea is asserted, for example, by pragmatists, representatives of a trend in idealist philosophy which is especially widespread in the United States. Such an understanding of truth leads pragmatists to justify the reactionary actions of contemporary capitalism. Since the exploitation of the workers, imperialist wars and plunder of less developed countries are of benefit, and bring profit to the capitalists, they are, from the pragmatists’ viewpoint, true and natural.

p Usefulness, however, cannot serve as a criterion of truth. On the contrary, only true knowledge brings benefit to mankind. Man can rely in his practical work only on true correct knowledge; only truth can bring him the results he expects. Therefore, if man, acting on the knowledge gained, reaches during his practical activity the aim he set himself, obtains the expected results, this signifies that his 170 knowledge corresponds to reality, is true.

p Here is one example. More than half a century ago, the Russian scientist Konstantin Tsiolkovsky developed the scientific theory of rocketry. He expressed the unusually bold idea, a truly fantastic idea at that time, that rockets could be used for flights to other celestial bodies. “Man will take a rock from the Moon,” Tsiolkovsky wrote more than half a century ago.

p It took a great deal of effort to turn Tsiolkovsky’s brilliant ideas into reality. The first artificial satellite of the Earth which was launched from a Soviet cosmodrome, Yuri Gagarin’s first orbital flight, and the flights of Soviet and US space stations paved the way for the first landing on the Moon of a piloted spaceship. This took place on July 20, 1969. Several hours after the landing Neil Armstrong and Adwin Aldrin set foot on the lunar surface and took the first samples of moonrock and dust. This was practical confirmation of Tsiolkovsky’s ideas, ideas that had seemed fantastic in their time.

Social theories and ideas too are tested in practice, in the revolutionary struggle of classes, the political activities of states, of various parties, and in the struggle of the peoples for peace and progress. The truth of the MarxistLeninist theory is being confirmed by life itself, by the practical activities of the international working-class and communist movement and by the struggle of the imperialistoppressed peoples for national and social liberation. The irrepressible movement of mankind from capitalism to communism offers incontrovertible proof of the great vital force, the great truth of the Marxist-Leninist teaching.