While it is true that for a certain theory to have a lasting influence on the human mind it must have a highly scientific value, yet this in itself is not enough. It quite often happened that a scientific theory was of utmost importance to science, nevertheless, with the probable exception of a few learned men, it evoked no interest whatsoever. Such, for instance, was Newton’s theory of gravitation. This theory is the foundation of astronomy, and it is owing to this theory that we have our knowledge of heavenly bodies, and can foretell the arrival of certain planets and eclipses. Yet, when Newton’s theory of gravitation made its appearance, a few English scientists were its only adherents. The broad mass paid no attention to this theory. It first became known to the mass by a popular book of Voltaire’s written a half century afterwards. There is nothing surprising about this. Science has become a specialty for a certain group of learned men, and its progress concerns these men only, just as smelting is the smith’s specialty, and an improvement in the smelting of iron concerns him only. Only that which all people can make use of and which is found by everyone to be a life necessity can gain adherents among the large mass. When, therefore, we see that a certain scientific theory stirs up zeal and passion in the large mass, this can be attributed to the fact that this theory serves them as a weapon in the class struggle. For it is the class struggle that engages almost all the people. This can be seen most clearly in Marxism. Were the Marxian economic teachings of no importance in the modern class struggle, then none but a few professional economists would spend their time on them. It is, however, owing to the fact that Marxism serves the proletarians as a weapon in the struggle against capitalism that the scientific struggles are centered on this theory. It is owing to this service that Marx’s name is honored by millions who know even very little of his teaching, and is despised by thousands that understand nothing of his theory. It is owing to the great role the Marxian theory plays in the class struggle that his theory is diligently studied by the large mass and that it dominates the human mind.