commodities at any time or place as proportioned to the state of their supply compared with the demand at that time and place, it is evident that the quantity of labour of the same time and place which any commodity, or parcels of commodities, will command, can alone represent and measure the state of the supply of them as compared with the demand,[87] and their values as founded on this relation. Thirdly: It has often been stated that the value of a commodity is determined by the sacrifice which people are willing to make in order to obtain it; and this seems to be perfectly true. But the question recurs, how are we to measure this sacrifice? It is obvious that we cannot measure it by the _quantity_ of another commodity which we are willing to give in exchange for it. When I give more calicoes, or more potatoes, than I did before, for a certain quantity of hardware, it does not at all follow that I make a greater sacrifice in order to obtain what I want. On the contrary, if calicoes and potatoes had both fallen in price, the one from improved machinery and the other from the abundance of the season, my sacrifice might even have been less rather than greater. Even the quantity of money which is given for a commodity is no measure of the sacrifice made to obtain it. Though it is an excellent measure of the variations in the sacrifice made, at the same time and place; yet without further information, it will tell us nothing either about the amount, or the variations at different places and times. The giving of an ounce of silver was a very different sacrifice in the time of Edward I. from what it is at present. It is obvious, therefore, that the sacrifice which we are willing to make, in order to obtain a particular commodity, is not proportioned to the _quantity_ of any other commodity for which it will exchange, but to the difficulty with which such quantity, whether more or less, is attained. Now labour can measure this difficulty, but nothing else can. If, then, the value of a commodity be determined by the sacrifice which people are willing to make in order to obtain it, it is the labour given for a commodity, and labour alone, which can measure this sacrifice.