By their nature and purpose different economic theories make almost opposite assumptions and use entirely different conceptions or aspects of time. These contrasting assumptions, which occur frequently, are essential to the nature of the various theories and cannot therefore be combined into a general theory. Coherence can only be obtained by an explicit scheme in which these theories are ordered to each other.||In this book Professor Shackle seeks a single, unified and coherent basis which would serve for all economic theories, particularly in regard to their treatment of time and to the possibility of acquiring the knowledge on which these theories are based. He examines five main approaches to economic analysis: a pure general equilibrium; Marshall's science of economic evolution; Keynes's `Kaleido-statics'; the models of economic growth devised by Harrod and Hicks; and Leontiefs input-output analysis. These basically divergent theories cannot be combined and must be ordered to each other.||Professor Shackle's examination of these modern theories and models will be of interest to economists attempting to find coherence in the diversity of economic theory.