g, therefore, to restrain the price (and the
rent) of land from rising indefinitely, and without limit, if the
demand for it should continue to increase. Conversely, if the demand
for land falls off, there is nothing to check the consequent fall in
price and rent. In the case of ordinary commodities, the supply would
be diminished, because most things are either consumed by being used,
or wear out in the course of time, and a regular annual production is
therefore necessary to sustain their supply at the existing level. But
land remains, whether it is used or not; and its supply is, broadly
speaking, just as incapable of being diminished, as it is of being
increased. Changes in the demand for land in either direction are thus
likely to affect its price in a much greater degree than that in which
the price of an ordinary commodity will be affected by a corresponding
change in its demand.

For most purposes, however, it is of more interest to compare land
with other agents of production, especially with capital and labor,
rather than with ordinary commodities. Now, as we have already noted,
there is some doubt as to the manner in which the supply of capital or
labor is likely to be affected by alterations in demand price. But the
supply of capital and the supply of labor, even if we suppose them to
be as entirely unresponsive to price changes as is the supply of land,
are at any rate not fixed. Not only _may_ they vary for many reasons,
but they are in fact likely to vary in direct proportion to the
population. An increase in population implies an increase in the
supply of labor; and it is likely to be accompanied by an increase in
the supply of capital; in other words, the supply of these agents will
expand, as the demand for them expands. But the supply of land will
remain what it was. This fact is enormously important in connection
with the broad problem of population, which will form the theme of
Volume VI.

But it is important also in other connections. It has been the
dominating factor in many absorbing controversies upon high policy
regarding the ownership of land, or the taxation of land values, upon
which we can touch but lightly here. It has seemed to many writers a
reasonable proposition to lay down, that the ordinary course of the
progress of society, the increase of population and industry, must
mean, as a broad general rule, a constant increase in the demand for
land. And, if that be granted, it seems to f