Fourthly. Apart from the fact that the stage of development reached at any time by the population and capital increase sets certain limits, even though elastic, to the extension of cultivation, and apart from chance effects which temporarily influence the market-price — such as a series of good or bad seasons — the extension of agriculture over a larger area depends on the overall state of the capital market and business conditions in a country. In periods of stringency it will not suffice for uncultivated soil to yield the tenant an average profit — no matter whether he pays any rent or not — in order that additional capital be invested in agriculture. In other periods when there is a plethora of capital, it will pour into agriculture even without a rise in market-price if only other normal conditions are present. Better soil than hitherto cultivated would in fact be excluded from competition solely on the basis of unfavourable location, or if hitherto insurmountable obstacles to its employment existed, or through chance. For this reason we should only concern ourselves with soils which are just as good as those last cultivated. However, there still exists the difference in cost of clearing for cultivation between the new soil and the one last cultivated. And it depends upon the level of market-prices and credit conditions whether this will be undertaken or not. As soon as this soil then actually enters into competition, the market-price will fall once more to its former level, assuming other conditions to be equal, and the new soil will then yield the same rent as the corresponding old soil. The assumption that it does not yield any rent is proved by its advocates by assuming precisely what they are called upon to prove, namely that the last soil did not yield any rent. One might prove in the same manner that houses which were the last built do not yield any rent for the building outside of house-rent proper, even though they are leased. In fact, however, they do yield rent even before yielding any house-rent, when they frequently remain vacant for a long period. Just as successive investments of capital in a certain piece of land may bring a proportional surplus and thereby the same rent as the first investment, so fields of the same quality as those last cultivated may bring the same proceeds for the same cost. Otherwise it would be altogether inexplicable how fields of the same quality are ever brought successively under cultivation; it seems that either it would be necessary to take all together, or rather not a single one of them, in order not to bring all the remaining ones into competition. The landlord is always ready to draw a rent, i.e., to receive something for nothing. But capital requires certain conditions to fulfil his wish. Competition between pieces of land does not, therefore, depend upon the landlord desiring them to compete, but upon the capital existing which seeks to compete with other capitals in the new fields.