From that time forward Socialism was no longer an accidental discovery of this or that ingenious brain, but the necessary outcome of the struggle between two historically developed classes--the proletariat and the bourgeoisie. Its task was no longer to manufacture a system of society as perfect as possible, but to examine the historico-economic succession of events from which these classes and their antagonism had of necessity sprung, and to discover in the economic conditions thus created the means of ending the conflict. But the Socialism of earlier days was as incompatible with this materialistic conception as the conception of Nature of the French materialists was with dialectics and modern natural science. The Socialism of earlier days certainly criticised the existing capitalistic mode of production and its consequences. But it could not explain them, and, therefore, could not get the mastery of them. It could only simply reject them as bad. The more strongly this earlier Socialism denounced the exploitation of the working-class, inevitable under Capitalism, the less able was it clearly to show in what this exploitation consisted and how it arose. But for this it was necessary--(1) to present the capitalistic method of production in its historical connection and its inevitableness during a particular historical period, and therefore, also, to present its inevitable downfall; and (2) to lay bare its essential character, which was still a secret. This was done by the discovery of _surplus-value_. It was shown that the appropriation of unpaid labor is the basis of the capitalist mode of production and of the exploitation of the worker that occurs under it; that even if the capitalist buys the labor-power of his laborer at its full value as a commodity on the market, he yet extracts more value from it than he paid for; and that in the ultimate analysis this surplus-value forms those sums of value from which are heaped up the constantly increasing masses of capital in the hands of the possessing classes. The genesis of capitalist production and the production of capital were both explained. These two great discoveries, the materialistic conception of history and the revelation of the secret of capitalistic production through surplus-value, we owe to Marx. With these discoveries Socialism became a science. The next thing was to work out all its details and relations. III