A) Economic categories are only the theoretical expressions, the abstractions of the social relations of production. M. Proudhon, holding this upside down like a true philosopher, sees in actual relations nothing but the incarnation of the principles, of these categories, which were slumbering — so M. Proudhon the philosopher tells us — in the bosom of the "impersonal reason of humanity".

M. Proudhon the economists understands very well that men make cloth, linen, or silk materials in definite relations of production. But what he has not understood is that these definite social relations are just as much produced by men as linen, flax, etc. Social relations are closely bound up with productive forces. In acquiring new productive forces men change their mode of production; and in changing their mode of production, in changing the way of earning their living, they change all their social relations. The hand-mill gives you society with the feudal lord; the steam-mill society with the industrial capitalist.

The same men who establish their social relations in conformity with the material productivity, produce also principles, ideas, and categories, in conformity with their social relations.

Thus the ideas, these categories, are as little eternal as the relations they express. They are historical and transitory products.

There is a continual movement of growth in productive forces, of destruction in social relations, of formation in ideas; the only immutable thing is the abstraction of movement — mors immortalis.

B)  The bourgeoisie begins with a proletariat which is itself a relic of the proletariat of feudal times. In the course of its historical development, the bourgeoisie necessarily develops its antagonistic character, which at first is more or less disguised, existing only in a latent state. As the bourgeoisie develops, there develops in its bosom a new proletariat, a modern proletariat; there develops a struggle between the proletarian class and the bourgeoisie class, a struggle which, before being felt, perceived, appreciated, understood, avowed, and proclaimed aloud by both sides, expresses itself, to start with, merely in partial and momentary conflicts, in subversive acts. On the other hand, if all the members of the modern bourgeoisie have the same interests inasmuch as they form a class as against another class, they have opposite, antagonistic interests inasmuch as they stand face-to-face with one another. This opposition of interests results from the economic conditions of their bourgeois life. From day to day it has becomes clearer that the production relations in which the bourgeoisie moves have not a simple, uniform character, but a dual character; that in the selfsame relations in which wealth is produced, poverty is also produced; that in the selfsame relations in which there is a development of the productive forces, there is also a force producing repression; that these relations produce bourgeois wealth — i.e., the wealth of the bourgeois class — only by continually annihilating the wealth of the individual members of this class and by producing an ever-growing proletariat.

The more the antagonistic character comes to light, the more the economists, the scientific representatives of bourgeois production, find themselves in conflict with their own theory; and different schools arise.

C) Just as the economists are the scientific representatives of the bourgeois class, so the Socialists and Communists are the theoreticians of the proletarian class. So long as the proletariat is not yet sufficiently developed to constitute itself as a class, and consequently so long as the struggle itself of the proletariat with the bourgeoisie has not yet assumed a political character, and the productive forces are not yet sufficiently developed in the bosom of the bourgeoisie itself to enable us to catch a glimpse of the material conditions necessary for the emancipation of the proletariat and for the formation of a new society, these theoreticians are merely utopians who, to meet the wants of the oppressed classes, improvise systems and go in search of a regenerating science. But in the measure that history moves forward, and with it the struggle of the proletariat assumes clearer outlines, they no longer need to seek science in their minds; they have only to take note of what is happening before their eyes and to become its mouthpiece. So long as they look for science and merely make systems, so long as they are at the beginning of the struggle, they see in poverty nothing but poverty, without seeing in it the revolutionary, subversive side, which will overthrow the old society. From this moment, science, which is a product of the historical movement, has associated itself consciously with it, has ceased to be doctrinaire and has become revolutionary.