Karl Marx,
A Contribution to the Critique of Political Economy
(1904)
“ If the productivity of labor declines, more time will be required for the production of the same use-value. Thus, the labor-time contained in a commodity or its exchange-value is a variable quantity, increasing or diminishing in an inverse ratio to the rise and fall of the productivity of labor. The productive power of labor which is applied in the manufacturing industry on a predetermined scale depends in the agricultural and extractive industries also on natural conditions which are beyond human control. ”
