tive loss; but if it is so used, nobody gets any income
from it. It has no power to enter in a really productive way into
combination with labor and capital, for it cannot so combine with them
as to add anything to those marginal products which the labor and
capital could create if they remained detached from it.

_The Universality of the Test of Rent._--This test, whether an
instrument can or cannot add something to the marginal product of
labor and capital, may be universally used. It may be applied to
everything that is made as an aid to labor. There are no-rent
buildings, locomotives, cars, tracks, ships, wagons, furnaces,
engines, boilers, and, in short, instruments of every description that
figure in production. Combine any one of them with labor and capital
and see what you get out of the combination; then take the labor and
capital away and see what they will produce as marginal labor and
capital; and the difference between the two amounts, whatever it is,
is the rent of the instrument. If the difference is _nil_, the
instrument is at the point of being abandoned.[1]

[1] Whether such an instrument should or should not be
called a capital good is a question of mere nomenclature; but
in this treatise we consider that every part of what we term
capital produces an income, and therefore a no-rent
instrument is not a capital-constituting good--otherwise
termed a capital good.

_True Capital rather than Capital Goods moved in Making such Tests of
Productivity._--In applying these tests with scientific accuracy we
should take away the true _capital_ used in connection with a
rent-paying instrument and use it as marginal capital elsewhere,
rather than take away the particular concrete thing in which that
capital is now embodied. In the case of the ship the accurate test is
made, not by taking stores, etc., bodily out of it and putting them
into other ships, but by letting the stores first earn what they can
where they are, converting the earnings into money, and, when the
stores are completely used up, spending the money to procure marginal
additions to the outfit provided for the other ships.

_One Difference between Land and Artificial Capital Goods._--In the
case of land a particular area is marginal or no-rent land, and, in a
static state, it remains so. Any particular ship, wagon, engine, or
other made tool begins its career as a rent payer and ends it as a
no-rent instrument. If we wa