Continuing to lay the foundations for an understanding of function time in economic theory, Rohatinski synthesises models addressing the circular character of economic activity, which passes through four general phases: production, distribution, exchange, and consumption. In models of simple reproduction, these phases are repeated indefinitely with no change in volume, while in extended reproduction the volume could expand or contract. The author examines the relations in this circular flow of economic activity among the three forms for capital identified by Marx: money capital, production capital, and commodity capital.