Firstly, because men are not free to choose one mode of production or another, because as every new generation enters life it finds productive forces and relations of production already existing as the result of the work of former generations, owing to which it is obliged at first to accept and adapt itself to everything it finds ready-made in the sphere of production in order to be able to produce material values.

Secondly, because, when improving one instrument of production or another, one clement of the productive forces or another, men do not realize, do not understand or stop to reflect what social results these improvements will lead to, but only think of their everyday interests, of lightening their labor and of securing some direct and tangible advantage for themselves.

When, gradually and gropingly, certain members of primitive communal society passed from the use of stone tools to the use of iron tools, they, of course, did not know and did not stop to reflect what social results this innovation would lead to; they did not understand or realize that the change to metal tools meant a revolution in production, that it would in the long run lead to the slave system. They simply wanted to lighten their labor and secure an immediate and tangible advantage; their conscious activity was confined within the narrow bounds of this everyday personal interest.

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Up to a certain period the development of the productive forces and the changes in the realm of the relations of production proceed spontaneously independently of the will of men. But that is so only up to a certain moment, until the new and developing productive forces have reached a proper state of maturity After the new productive forces have matured, the existing relations of production and their upholders – the ruling classes – become that "insuperable" obstacle which can only be removed by the conscious action of the new classes, by the forcible acts of these classes, by revolution. Here there stands out in bold relief the tremendous role of new social ideas, of new political institutions, of a new political power, whose mission it is to abolish by force the old relations of production. Out of the conflict between the new productive forces and the old relations of production, out of the new economic demands of society, there arise new social ideas; the new ideas organize and mobilize the masses; the masses become welded into a new political army, create a new revolutionary power, and make use of it to abolish by force the old system of relations of production, and to firmly establish the new system. The spontaneous process of development yields place to the conscious actions of men, peaceful development to violent upheaval, evolution to revolution.