The main key to the economics of the postwar world is a simple truism — that the rate of accumulation is equal to the rate of production less the rat… - Kenneth E. Boulding

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The main key to the economics of the postwar world is a simple truism — that the rate of accumulation is equal to the rate of production less the rate of consumption. This is the "Bathtub Theorem." Production may be likened to the flow of water from the faucet, consumption to the flow down the drain. The difference between these two flows is the rate at which the water in the bathtub - the total stockpile of all goods - is accumulating.
War drains the economic bathtub in a great waste of consumption. The first problem of reconstruction is to rebuild the stockpile. It can be rebuilt only by widening the gap between production and consumption, or, in the case of a single country, by importing more than is exported. It is difficult for a ravaged country to increase either its production or its net imports. Unless it can obtain outside help, therefore, it must suffer a drastic restriction of consumption. Frequently the only way consumption can be restricted is by inflation. Here, therefore, is the key to the most fundamental problems of reconstruction.