This quantity of labour is no constant factor. New inventions, improvements in labour processes, increase in the productivity of labour, etc., cause a diminution in the quantity of labour necessary for the reproduction of a commodity; its exchange value, or expressed in terms of money, its price, will therefore sink, provided that other things (demand, medium of exchange) remain equal. Consequently, labour is the source of exchange value, and the latter is the principle which regulates exchange operations. Exchange value even measures the extent of the commodity wealth of society. Wealth may increase in volume, but decrease in value, in so far as a less quantity of socially necessary labour becomes necessary for its reproduction. The more progressive a country is industrially and the higher the level of its civilisation, the greater is its wealth, and the smaller is the quantity of labour which must be expended on the creation of wealth. In the practical Labour politics of our times, this is expressed in higher wages and shorter working hours. It was said above that use value is a basic condition for the exchange of the individual commodity. This does not exhaust the role of use value. The quantity of use value of which society has need determines the quantity of the exchange values to be created. If more commodities are required than society requires, the superfluous commodities have no exchange value, in spite of the labour that is expended on them.--("Capital" (German), Vol. III., 1, pp. 175-176.) The complete realisation of exchange values or the social labour that is performed depends, as is seen, on the adaptation of supply to demand, and is a matter of organisation, of social direction. We have noticed that the Marxian theory of value is related to that of the classical economists, but they are by no means the same thing. Apart from some improvements and definitions which Marx made, they are distinguished by the following conceptions: In the classical theory of value, the capitalist who directs production and provides with his capital the tools and raw materials of labour, markets the finished commodity, and keeps going the processes of reproduction, appears as the only creator of value: the wage worker is only one of his means of production. In the Marxian theory of value, on the other hand, the wage worker who transforms the raw materials into commodities, or removes the raw materials to the place of production, appears as the sole creator of value. Value is only created by the worker in production, and in distribution connected therewith. 3. _Wages and Labour._