respect to the market; and therefore their broad result is to postpone the consequences of the operation of the law of diminishing returns on the one hand, and on the other to reduce the amount of the differential advantages of situation of different soils. In both these ways they tend to arrest the rise of rent.
They may exercise a further influence. As a consequence of changes in the markets to which the produce of the land is sent, and of fresh demands in those new markets, they may lead to the raising of different crops from those produced before. These crops may of course be less suited to the character and conditions of the land in question; but the balance of probability seems to incline to the conclusion that, with the extension of the number of available markets, and of the area from which the supplies for one particular market are drawn, crops will tend more and more to be raised from the soils which are best fitted to produce them, and to take their place in the most suitable and productive order of rotation. In this way, again, the practical consequences of the law of diminishing returns are postponed, and the differential advantages of different soils confined within a smaller range. The increase of rent is arrested, and what was in one place an increment becomes a decrement, and in another a decrement is converted into an increment.
All these changes allow of the advance of wages and profits; and in these several ways the problem, so simple in Ricardo's hands, becomes very complex. It might be cogently argued that the broad result is to point to a fall rather than to a rise of rent, so far, at any rate, as the agricultural rent of the old countries of the world is concerned; and it is at least certain that the measurement of differential advantages from different standpoints renders the existence in particular instances, or continuance, of an increment, or decrement, as the case may be, very doubtful and difficult to determine. Nor is this latter conclusion untrue of the circumstances of urban land; for changes in fashion, or the methods of business or transport, assuredly affect the relative values of different sites, lowering some while raising others. It is even conceivable that improvements in the means of conveyance may, taking a general view, diminish as well as increase the advantages of central sites; and that some industrial or inventive change in the future may arrest the tendency to concentration in towns, and reawaken the industries of country villages.
But, even if an increment be regarded as probable, the difficulty remains of determining how much of it is unearned, and how much is earned. Ricardo himself defined rent as 'that portion of
