Marshall argued that the forces of both demand and supply determine value, with demand determining price and output in the short run and changes in resource inputs and production costs influencing price in the long run. He suggested that supply prices would depend upon production costs and in analysing short-run production cost showed how the marginal product of all resources tends to diminish as variable factor inputs are combined with fixed amounts of other resources (DIMINISHING RETURNS to the variable factor input). In the long run, Marshall suggested that industries would experience reducing costs and prices because of ECONOMIES OF SCALE resulting from greater specialization. See REPRESENTATIVE FIRM.