Isolation and Aggregation in Economics

In explaining economic phenomena, economic analysis concentrates on selected influences and fixes the host of other factors under a ceteris paribus clause. This view, which goes back to Alfred Marshall (1842-1924), is developed in the first part of the book. Aggregation is viewed as a particular application of ceteris paribus analysis - isolation from "structural effects". This leads to an approach, called "closed aggregation", which was introduced by Kenneth May and is also implicit in Keynes' writings but has been neglected more recently. It is argued that macroeconomic models are more stable and more general than the corresponding micro models and that there is no simple analogy between them.