The error in the text cited is fundamental, but not unique. It is representative of most standard text. Heilbroner and Thurow have the virtue of clear expression – a virtue that makes it easier to spot errors. Other texts leave the student with the same erroneous impression, but without forthrightly stating the implication in words that cause us to think again. Nor is the error confined to standard economists, Karl Marxs madels of simple and expanded reproduction are also isolated circular flow models.