adaptations and improvements of the original resources by which men
fit nature better to do their will. These two (a and b) become
more and more difficult to distinguish in settled and civilized
communities, and become blended into one mass of valuable objects, the
wealth of the nation.

(c) The social system under which men live together, make use of
wealth and of their own services, and exchange economic goods.

(d) The people, considered with reference to their number, race,
intelligence, education, and moral, political, and economic capacity.

The particular economic problems which are presented to each
generation of our people are the resultant of all these factors taken
together. A change in any one of them alters to some extent the
nature of the problem. The problems change, for example, (a) with the
discovery or the exhaustion (or the increase or decrease) of any
kind of basic material resources; (b) with the multiplication or
the improvement of tools and machinery or the invention of better
industrial equipment; (c) with changes in the ideals, education, and
capacities of any portion of the people whether or not due to changes
in the race composition of the population; (d) with the increase or
decrease of the total number of people, and the consequent shift in
the relation of population to resources. Many examples of such changes
may be found in American history, and some knowledge of them is
necessary for an appreciation of the genesis and true relation of our
present-day problems.

§ 4. #Attempts to summarize the nation's wealth.# If we seek to
compare the material resources of the nation at one period in our