22

ECONOMIC PRINCIPLES

urgency of the desires left unsatisfied grows less as increase
of supplies enables us to meet the progressively diminishing
cravings for the satisfactions which the commodity can
render. If we designate the least urgent of the desires
which can be satisfied with any given amount of the
commodity “the marginal desire,” we can enunciate the
principle that the intensity of the marginal desire for the
commodity decreases as the supply of the commodity
increases. The principle is otherwise phrased thus: The
marginal utility of a commodity decreases as its supply
increases.
[f we consider, not one person, whose cravings are
gradually satiated, but a group or community, the application
of the principle is not less general, though some exception
may be taken to the form in which it is expressed. The
direct comparison of the urgency of the needs of different
persons for any commodity is not feasible. We can only
compare the offers made by different persons for additional
supplies of a commodity. The amounts offered by different
persons are affected, not only by differences in intensity of
desire for the commodity, but also by differences in the
amounts of other goods which they possess, and can offer in
expression of their desires, Expressed in terms of money,
such offers are known as “demand prices,” and the principle
previously enunciated takes the form: The marginal demand
price of a commodity decreases as the amount already
supplied increases.
It should be remarked at once that this phrase has no
reference to changes which result from lapse of time. Lapse
of time is, indeed, associated with change in the kind and
amount of consumption desired by a person or community.
But such changes, so far as they result from changes in the
disposition of the person or community, are not here in
contemplation. The statement is merely that, the needs
for, and capacities for appreciation of, the different supplies
of the commodity which can be conceived of, being what they
are, the greater the actual supply, the less the marginal
demand price, that is, the less the urgency of desire for
further supplies.