The topic of economies and size bears some resemblance to the (present-day) topic of economies of scale . The reader is warned that there are differences as well as similarities, to say nothing of the usual penumbra of obscurity which perhaps more clearly than anything else distinguishes the economics of Alfred Marshall from the Marshallian economics which is built upon it. Marshall, as Schumpeter explains , 'blurred the clarifying distinctions between falling cost curves and downward shifts of cost curves and between costs that fall while production functions stay put and costs that fall in consequence of changes in production functions'. I Marshall, Schum peter might usefully have added , blurs most other distinctions as well. Marshall's reply would probably have been that reality, unlike theory, does not always lend itself to the rigorous categorisations of the pure logician , and that the first duty of the economist is to be faithful to the viscosity and plasticity of the world outside the mind.