"The danger of tautological propositions is considerable in discussions of the concept of normal profits. Because supernormal profits seem to invite newcomers to an industry and sub-normal profits seem to drive away those who are in an industry, some writers are inclined to define normal profits as the earnings of the fixed resources in an industry which neither grows nor declines in size or number of firms. It should be clear that such a definition is useless: it muddles together attractiveness and actual afflux, desirbility of entry and ease of entry, zero profits and monopoly rents."

-- Fritz Machlup

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