RENT 
205 
conveyed along costly aqueducts. To be 
strictly logical, if we take the narrower view 
of rent, we ought to say that the marginal 
land earns its marginal worth (a scarcity 
price) and not rent, but that super-marginal 
land earns its marginal worth plus an 
extra sum (differential rent) which measures 
the differential advantages enjoyed by it, that 
is to say, a sum which would render the substi 
tution of that land for marginal land a matter 
of indifference. 
It goes without saying that the payment 
for land of a sum representing its marginal 
worth is a phenomenon foreign to our ex 
perience. Even under conditions of such a 
kind that a community is dependent for its 
food upon the produce of its own country, it 
will generally be found that there is some land 
of some quality, though it may be of a very 
low quality and very inconveniently located, 
which has not yet been brought under the 
plough or used for grazing. And when we 
come to modern conditions wherein all 
parts of the world are linked together by 
international trade, we find unlimited tracts 
of unoccupied land available for the pro 
duction of the food supply of the future 
population. Hence it is readily comprehen 
sible why it is that in economic writings