138 ECONOMIC ESSAYS IN HONOR OF JOHN BATES CLARK 
(d) Clark correspondingly widened the meaning and applica- 
tion of the term rent beyond that of the orthodox English 
economics, making it apply to the “sums earned by outward and 
material instruments of production” of any and every kind, u.e., 
the earnings of concrete capital. The rent law is universal. 
(e) Clark called the earnings of “pure capital” interest, and 
he conceived of this as rent (value) expressed as a percentage of 
the value of the abstract capital. Thus interest, as Clark wished 
to express it, did not consist of uses, yields, earnings, or incomes 
other than those composing rents, but simply was rent, expressed 
as a price in relation to the price of the instruments that embody 
the fund. 
That these ideas appeared at that time to be radical novelties 
in American and English economic theory, is evident. The vigor 
and incisiveness of their statement helped them to command 
immediate attention even from those who were not ready to 
accept them as true. It must have been obvious that their 
acceptance would involve sweeping changes in the structure of 
the then accepted theory of distribution, with its sharp division 
between (natural) land and (artificial) capital as factors of pro- 
duction, and between rent (of land) and interest (on capital) as 
forms of “earnings” or incomes. Clark himself began at once to 
shape and build a structure of distributive theory but faintly 
forecast in his earlier essays, and increasingly to this day these 
ideas have exercised an influence upon theoretical opinion. 
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2. Possible Sources; the American Tradition 
Ideas departing so far from prevalent opinion rarely if ever 
spring as pure inventions of the moment from one mind. Nor 
does a change in the content and direction of an individual’s 
thought, as marked as that of Clark at that time, occur without 
some influence from other thinkers or from environing conditions. 
But to trace such influences to their sources seems, in the case of 
Clark, at first unusually difficult. His literary style is didactic 
rather than polemical, and his thought seems to move along 
positive lines hardly at all conscious either of his forerunners 
or of hostile opinions, once he has formulated his own views. 
His writings give slight internal evidence of the sources of his 
thought. In the monograph in question the only references to the 
opinions of others are in minor matters, in three cases dissenting,