202 
POLITICAL ECONOMY 
A with its produce of 60 bushels will rise to 45, 
that is 60 minus 15, on the assumption that 
the whole of the lowest quality of land is not 
in use. The significance of this assumption 
will be brought out in due course. 
We may pause to underscore what is 
outstanding in this reasoning, namely, that 
it is the operation of the law of sub 
stitution, or indifference, among competing 
persons which brings about the payment of 
rent in the circumstances supposed. Pay 
ments are made for land because effective 
tendencies to substitute what is lying idle 
for what is used, and what is cheap for what 
is dear, are at work. These effective tenden 
cies at first create the rent, and then lever it 
up until it becomes such in amount that any 
further substitution is a matter of indifference. 
So we may affirm that the rent of land is 
the payment which equalises the earnings of 
cultivators of the same capacity, thus leaving 
them indisposed to substitute one piece of 
land for another. 
In order to complete our theory in its first 
rough-hewn form it is necessary to consider 
what would happen if the whole of the land 
were absorbed and the population still grew. 
Let a state of affairs be given in which all the 
land is in use, but the worst only just in use,