Kapitaltheorie

Kapitaltheorie, or capital theory, is the branch of economic theory that studies capital as a factor of production, the nature of capital goods, and the processes by which capital is accumulated, measured, and allocated within an economy. It covers theories of capital formation, the determination of interest, and the role of capital in growth and distribution.

Historically, it developed from classical political economy through marginalist and neoclassical approaches, and also in Marxian analysis. Classical theory treats capital as produced means of production that enables longer, more productive processes; saving converts consumption goods into capital goods, and the return to capital arises from the productivity of these goods and from time preference.

In neoclassical capital theory, capital is a produced, durable input with a marginal product. The equilibrium capital stock adjusts to the interest rate, prices, and technology, and capital deepening occurs when investment raises output per worker. The concept of capital is central to production functions such as Y = F(K, L).

Measurement and the nature of capital have been disputed. Capital is a heterogeneous structure of goods, not a single homogeneous input. The Cambridge capital controversy argued that aggregate capital cannot be measured independently of distribution, complicating the link between investment and macroeconomic output.

Marxian capital theory treats capital as a social relation of production and emphasizes the circuit of capital, M-C-M', and the extraction of surplus value within capitalism.

In contemporary economics, capital theory underpins growth models (Solow, endogenous growth) and informs policy on investment, depreciation, and capital formation.