120 ECONOMIC PRINCIPLES

will be clear that the question of the amount of his net
product is one which is not concerned with himself personally,
but that any one of those who could replace him, or whom
he could replace, must be regarded as having the same net
product. If the addition of one to the group add a certain
amount to its total product, and it is indifferent which of
the group, thus enlarged, does the work of the added man,
then each in turn may be regarded as the last added, and
none can be assigned an importance superior to any
other.
Now let us give attention to the comparison of such net
products, of the members of a working group, as additions
are made to its numbers. We may find that the added
members continually add the same net product, or that the
addition falls off as the numbers grow, or the opposite, If
the additions are unchanged as the numbers increase, that
is, if we find something corresponding to constant returns,
this net product will be the measure of the value to the
employer of the assistance of each and every one of the
workmen. Should they be able to be hired for less, the
employer profits, while if they cannot be had for that
amount his immediate interests lie in the direction of not
seeking to hire them at all.
But a more general case will be found to be that in which
the increase of numbers, employed in a particular way, leads
to a decrease in the net addition made by each added to the
number. The net product of the marginal man decreases as
the number to be set at work increases. As already indicated,
the assumption that each may be substituted, without loss or
inconvenience, for any other, leads to the conclusion that the
net product of the marginal worker measures the value to
the employer of each of those with whom he is interchangeable.
 A further point of importance is, that the larger the
number for whom employment is to be found, the smaller
the marginal net product, and therefore the less the price it
is worth while offering for additional men. So long as the
current rate of wages is less than the marginal man’s product,
so long is there profit in securing additions to the number
employed. When that marginal product, in its process of