By the time it comes to interpretation of the substantive conclusions, the assumptions on which the model has been based are easily forgotten. But it… - Wassily Leontief

How will the cessation of war purchases of planes, guns, tanks, and ships … affect the national level of employment? How many new jobs will be created by the consumers’demand for an additional one million of passenger cars, how many of these jobs can be expected to be located in the automobile industry itself, and how many in other industries such as Steel and the Chemicals, the Coal and the Petroleum industries? How much additional freight traffic and revenue can the American railroads expect to derive from every billion dollars worth spent on post-war housing construction?

The statistical study presented in the following pages may be best defined as an attempt to construct, on the basis of available statistical materials, a of the United States for 1919 and 1929. One hundred and fifty years ago, when Quesnay first published his famous scheme, his contemporaries and disciples acclaimed it as the greatest discovery since Newton’s laws. The idea of general interdepence among the various part of the economic system has become by now the very foundation of economic analysis. Yet, when it comes to the practical application of this theoretical tool, modern economists must rely exactly as Quesnay did upon fictitious numerical examples.

The general, and at the same time dynamic, type of analysis still remains an unwritten chapter of economic theory, the claims of innumerable “model-builders” notwithstanding... The … theoretical approach, based on the combination of the complexities of a general interdependent system with the simplifying assumptions of static analysis, constitutes the background of this investigation.