Notice that it equals the ratio of the marginal product of capital to the average product of capital. Capital is, in this view, an abstract fund, the destiny of which is to migrate through an endless series of outward forms.The aim of this paper is to analyze John Bates Clark's influence in the passing of the. Investment is the change in capital stock during a period. Consequently, unlike capital, investment is a flow term and not a stock term. He developed marginal productivity theory and used it to explore the way income is distributed between wages, interest, and rents in a market economy. How many kinds of time are there in a capital-using economy? Moves the actual capital stock over time in response to changes in the desired stock. Labor costs, return on capital, Clark. 2010. Economic Record, 46 (December 1970), pp. 449-466.