... The basis of this negative relationship between the two variables was not clearly spelled out by the original marginalist authors and the plethora of approaches to the theory of investment, in the post-War era, can be seen-partly at least-to be the result of this original vagueness. Among the competing theories of investment, we can cite the "two stage approach" of Lerner (1944) and Haavelmo (1960), where the inverse relationship between the volume of investment and the rate of interest is due to the short-run rising supply price of capital goods; its microeconomic reinterpretation, the "adjustment costs approach" of Eisner and Strotz (1963), Gould (1968) and others, which-in contrast to Lerner and Haavelmo's analysis-still continues to be popular; the so-called "dynamic" "neoclassical theory of investment" of Jorgenson (1963Jorgenson ( , 1967 and Precious (1987), which also has lost its appeal even among the neoclassical economists; the 'q' theory of Tobin (1969Tobin ( , 1982 and Tobin and Brainard (1977), based on Keynes' theory of investment and, hence, popular among the Keynesians; and, despite its criticisms by By the 1930s, economists like Friedrich Hayek, Erik Lindahl and John Hicks began to see the problem more clearly, realising that conceiving capital as a given value magnitude, capable of changing its form en route to a long-run equilibrium, involved serious difficulties. 3 Conceiving capital as a given vector of heterogeneous goods � a la Walras, rather than a value magnitude, implied, on the other hand, a return to the problem that Walras himself had realised by the fourth edition of the El� ements: a long-run analysis, where a uniform rate of return on the supply price of the respective capital goods employed in the economy, is inconsistent with the data of the system assumed to be known prior to the analysis (i.e., the endowments, consumer preferences and technology), if the endowments include, as in Walras, a given quantity of each capital good (Garegnani 1990, 20). ...