For it is impossible to set aside the view that Marx's theory of value and surplus value has rather the significance of a political and social slogan than of an economic truth. It is for Marx the basis of the class struggle of the workers against the middle class, just as Ricardo's theory of rent was the basis of the class struggle of the bourgeoisie against the aristocracy, or as the doctrines of the social contract and of the natural rights of man formed the basis of the struggle of the middle classes against autocracy and divine right. Such militant philosophies need not in themselves be true, only they must accord with the sentiments of the struggling mass. It is with such philosophical fictions that human history works. Marx's theory of value explains neither the vast and unparalleled accumulation of wealth nor the movement of prices during the last sixty years. Wealth, measured in values, has, in the last few decades, increased by many times the increase in living labour-power. In this connection the old formula can be reversed: wealth increases in geometrical, living labour-power in arithmetical progression. The greatest difficulty in Marx is that the inventors and discoverers, the chemists and physicists, the pioneers and organisers of industry and agriculture, are not regarded by him as creators of surplus values. Thinkers, who by chemical researches and discoveries double the productive capacity of the soil and conjure forth values in millions from the waste products of industry: physicists who place new sources of power and new means of production at the disposal of mankind and multiply the productivity of labour; organisers who co-ordinate the forces of production and introduce new methods of working--all this creative and directive work, demanding, as it often does, an infinite amount of intensive intellectual effort, is not considered to increase the total sum of exchange values of the nation. However, as far as the distribution of products is concerned, Marx's theory is, generally speaking, correct; distribution is carried out under the capitalist economic system not according to the amount of productive work done, but in proportion to the outlay of capital and the skill in commercial manoeuvring which obtains in the sphere of circulation. Unique as an investigator of the laws of the proletarian movement, eminent and even a great pioneer as a sociologist, Marx is, in respect of economic theory, predominantly an agitator. His system, more than any other system of Socialism or of political economy, is the revolutionary expression of proletarian thought and feeling. His doctrines of value, surplus value, the economic determination of history, the evolution from Capitalism to Socialism, the political and economic class struggle, will for long have the force of truth for the masses and will continue to move them.