best to employ that nomenclature.
What is not uncertain is that these gains are measurable by the same
formula that measures the rent of a piece of land. If the essential
thing about rent were that it is a material product and consists of a
sum of differential quantities, these incomes certainly would be
rents. Popular thought, however, attaches another meaning to this
term, and we therefore limit ourselves to saying that these
differential incomes or surpluses may be determined in amount by the
principle of rent. They can be described and measured exactly as the
Ricardians described the income of landlords.[1]

[1] The term _rent_ has even been applied to surpluses of a
psychological kind. Certain gains that men get consist purely
in pleasures or in reduced pains or sacrifices, and a few
writers have applied to such subjective gains the term
_rent_. If a man buys a barrel of flour for five dollars and
gets out of it a service that is a hundred times as great as
he could get from some other article which he buys for the
same amount, this surplus of pleasure may be called, by a
figure of speech, "consumers' rent"; and if the essence of
rent were the fact that it can be made to take the form of a
surplus or difference, the name would be well chosen, though
there is danger that by this use of the term science may
divorce itself from practical thought and life. If we take
all the barrels of flour that a man uses in ten years, there
is one which is marginal, because it is worth to the man only
enough to offset the sacrifice he incurs in getting it. All
the others are worth more. We can arrange them in a scale in
the order of their importance, the most necessary one coming
first and the least important one last; and we can compare
the service which each one renders with that rendered by the
last, and measure the surplus of good which each one does to
the user. There is here in operation a law of diminishing
subjective returns. Early units consumed afford more pleasure
than do later ones. There results a series of surplus gains,
and the sum of all these surpluses makes a total of net
benefit,--is a gain that is not offset by a compensatory
sacrifice. The last barrel of flour on the list is worth just
what it costs, and all the others are worth more. They give
the consumer a surplus of satisfaction for which he