Even a decade after the end of the 1914-1918 war, economic theory assumed that the world was tranquil and orderly. By 1939 an economic slump without parallel, allied to the re-emergence of military ambition in Europe, had brought economic theorists face to face with reality. In this classic book, first published in 1967, Professor Shackle provides a study, in exact and professional language, of the precise nature, structure, presuppositions, language and inter-relations of the theories which were formulated in these fourteen years - unparalleled in the whole history of economics except perhaps by the years of the Physiocrats and Adam Smith. These theories are not prototypes on the way to something better but are of essential and permanent importance.