122 ECONOMIC PRINCIPLES

the marginal net produce of labour begins to decrease in
value if not in amount, and when expansion has passed this
point the preceding considerations apply. The renewal of
the increase may take place as the result of changes in
organisation, the application of newly discovered methods
of using scientific knowledge and the extension of such
knowledge, the discovery of natural resources hitherto
unknown, and the like. Thus the decrease of marginal
productivity of labour is not a feature precluding hope for
the future. It may simply connote a pause in the conflict
between man and nature, a pause limited in duration and in
the extent of the industrial field affected. Such pauses,
however, are an important feature in the situation, since
their limits are not easily foreseen. The insistence on
increase of remuneration on the part of hired workmen
cannot, in itself, provide the means of meeting the demand,
though it sometimes serves as a stimulus, urging to the
invention of some method of reversing the tendency to
decrease of marginal productivity of labour in industrial
employments.
Except in those branches of industry in which, for the
time, increased numbers can be employed to increasing
advantage, we may say that the net product of the marginal
labourer tends to decrease, and that the limit of the price
which employers can afford to offer for labour is marked by
this marginal productivity. This has been developed in
reference to labourers who are interchangeable between
themselves, but it can readily be extended to the more
general case of units not mutually equivalent. The employer
is concerned rather with the work done, or to be done, than
with the persons who are to do it. This statement must not
be distorted into meaning that it is indifferent to an employer
whether his work is done by many or by few hands. Clearly
that is not the case. Neither is it to be inferred that quality
of work is unimportant. What is intended is that the
application of the principles here discussed does not depend
on the comparison of individuals doing exactly equal amounts
of work. We are dealing with labour in quantities sufficiently
large for the use of a marginal unit of labour which shall be