If the theoretical explanations of growth currently to be found in the economic literature pay generally little attention to the role of demand factors in the long period, this appears to be due mostly to theoretical reasons. It is in fact the influence of the idea of the spontaneous tendency of the system toward the full utilization of available resources entailed by the traditional demand-and-supply explanation of value and distribution, rather than observation of the actual characteristics of economic development, that leads most economists to describe and account for growth in terms of the growth of resources over time and their productivity, with an exclusive focus on supply factors.