The methods of production have continuously changed with the progress of time. Whence came these changes? The manner of labor and the productive relationship depend upon the tools with which people work, upon the development of technique and upon the means of production in general. Because in the Middle Ages people worked with crude tools, while now they work on gigantic machinery, we had at that time small trade and feudalism, while now we have capitalism; it is also for this reason that at that time the feudal nobility and the small bourgeoisie were the most important classes, while now it is the bourgeoisie and the proletarians which are the classes. It is the development of tools, of these technical aids which men direct, which is the main cause, the propelling force of all social development. It is self-understood that the people are ever trying to improve these tools so that their labor be easier and more productive, and the practice they acquire in using these tools, leads their thoughts upon further improvements. Owing to this development, a slow or quick progress of technique takes place, which at the same time changes the social forms of labor. This leads to new class relations, new social institutions and new classes. At the same time social, i. e., political struggles arise. Those classes predominating under the old process of production try to preserve artificially their institutions, while the rising classes try to promote the new process of production; and by waging the class struggles against the ruling class and by conquering them they pave the way for the further unhindered development of technique. Thus the Marxian theory disclosed the propelling force and the mechanism of social development. In doing this it has proved that history is not something irregular, and that the various social systems are not the result of chance or haphazard events, but that there is a regular development in a definite direction. In doing this it was also proved that social development does not cease with our system, because technique continually develops. Thus, both teachings, the teachings of Darwin and of Marx, the one in the domain of the organic world and the other upon the field of human society, raised the theory of evolution to a positive science. In doing this they made the theory of evolution acceptable to the masses as the basic conception of social and biological development. III. MARXISM AND THE CLASS STRUGGLE.