198 ECONOMIC ESSAYS IN HONOR OF JOHN BATES CLARK 
namely: In a given situation, and within a given period, during 
which the standard of living is held constant, and the material 
means of production (tools, machines, and structures) undergo 
no substantial change in kind or quantity, is it possible by thrift 
(saving and industriousness) substantially to increase the rate of 
accumulation of concrete capital without putting increasing strain 
upon the agents and instruments of production at the moment 
existent and functioning, and thereby increasing the unit cost of 
accumulating capital? 
The results of my study were presented in three articles.” 
These called forth criticisms from Professor Bohm-Bawerk and 
Mr. James Bonar.” To my contentions relative to the cost of 
production of capital goods and the cause of interest I shall return 
presently. At this point I speak only of my contribution, if such 
it was and is, to the explanation of the effective nature and 
functioning of concrete capital and its relation to a possible escape 
from the economics of exploitation. 
Borrowing an idea from Francis A. Walker's definition of 
money I maintained that concrete capital is what concrete capital 
does. From this proposition it follows that not all “present 
goods” or “stocks” are capital goods, or capital goods in equal 
degree. They must be capitalized in a productive process and I 
undertook to show how. 
Bohm-Bawerk had shown in the Positive Theorie des 
Kapitales that capitalistic production differs from production 
by unaided human labor in being less direct, by reason of the 
interpolation of intermediate products between the beginning of 
labor and the completion of the final goods, and that such 
indirect production is more fruitful than direct production is 
because every intermediate product enlists the cooperation of an 
auxiliary force (einer Hilfskraft). What he had not shown, and 
what no writer before him had shown was, the specific thing that 
the intermediate product must be in order to enlist the coopera- 
tion of an auxiliary force. 
Starting from Spencer’s definition of life as a continuous adjust- 
ment of internal relations to external relations, I argued that pro- 
1 «Phe Cost of Production of Capital,” Quarterly Journal of Economics, 
Vol. ITI, July, 1889; “The Theory of Capital,” ibid., Vol. IV, January, 1890; 
and “The Growth of Capital and the Cause of Interest,” ibid. Vol. V, 
January, 1891. 
2 Quarterly Journal of Economics, Vol. IV, April, 1890.