“Of these, indeed, it may sometimes purchase a greater and sometimes a smaller quantity; but it is their value which varies, not that of the labour which purchases them. At all times and places, that is dear which it is difficult to come at, or which it costs much labour to acquire; and that cheap which is to be had easily, or with very little labour. Labour alone, therefore, never varying in its own value, is alone the ultimate and real standard by which the value of all commodities can at all times and places be estimated and compared. It is their real price; money is their nominal price only.
But though equal quantities of labour are always of equal value to the labourer, yet to the person who employs him they appear sometimes to be of greater, and sometimes of smaller value. He purchases them sometimes with a greater, and sometimes with a smaller quantity of goods, and to him the price of labour seems to vary like that of all other things.”