Now there can be little difficulty in seeing how the amount of rent of land is governed. That land will pay no rent at all which only gives produce enough to pay the wages of the labourers who work upon it, together with the interest of any capital which they require. The rent of better land will then consist of the surplus of its produce over that of the poorest cultivated land, after allowance has been made for the greater or less amount of labour and capital expended on it. Or we may look at the matter in this way: The price of corn is decided by the cost of producing it on land which just pays the expenses of cultivation, because when more corn is needed, it is from such land we must procure it, the better land having been long since occupied. But corn of the same quality sells at the same price whatever be its cost of production; hence the rent of more fertile land will be the excess of the price of its produce over that of land which only just pays the cultivator and leaves no rent. CHAPTER XI. EXCHANGE. #70. How Exchange Arises#. One of the most important ways in which we can increase wealth consists in exchange--#in giving what we do not want in return for what we do want#. Wealth, as we have seen, is anything which is actually useful to us, because we have not enough already, and which can be transferred to another person. But when our want of any kind of commodity is satisfied, we want no more of that, but we do want other kinds of commodity. The result is that exchange constantly produces a #gain of utility#. Some people have objected that there can be no good in exchange, because that which is given equals in value that which is received. Others have said that, if one party gains, it must evidently be by robbing the other party. According to this view, trade would consist in trying to beggar your neighbour. That which is given does really equal in value that which is received, but it does not equal it in utility, and to increase utility is the purpose of all production and all commerce. We do not pay for things in proportion to their usefulness, or else air and water would be the most costly of all things. A good-sized loaf may be bought for fourpence or sixpence, although bread is the staff of life. Before attempting to understand this apparent paradox, we must settle exactly what we mean by value.