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Page:Principles of Political Economy Vol 1.djvu/599

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§ 1. We have investigated the laws which determine the value of two classes of commodities: the small class which, being limited to a definite quantity, have their value entirely determined by demand and supply, save that their cost of production (if they have any) constitutes a minimum below which they cannot permanently fall; and the large class, which can be multiplied ad libitum by labour and capital, and of which the cost of production fixes the maximum as well as the minimum at which they can permanently exchange. But there is still a third kind of commodities to be considered: those which have, not one, but several costs of production: which can always be increased in quantity by labour and capital, but not by the same amount of labour and capital; of which so much may be produced at a given cost, but a further quantity not without a greater cost. These commodities form an intermediate class, partaking of the character of both the others. The principal of them is agricultural produce. We have already made abundant reference to the fundamental truth, that in agriculture, the state of the art being given, doubling the labour does not double the produce; that if an increased quantity of produce is required, the additional supply is obtained at a greater cost than the first. Where a hundred quarters of corn are all that is at present required from the lands of a given village, if the growth of population made it necessary to raise a hundred more, either by breaking up worse land now uncultivated, or by a more elaborate cultivation of the land already under the plough, the additional hundred, or some part of them at least,