The aim of every classification is to establish order in things and in thought. When this operation is applied in the sciences at a given time in their evolution, it provides a faithful though provisional picture of the scientific knowledge at that time. By enabling us to take such an inventory of our knowledge, classification provides a sort of spatiotemporal cross section of the sphere of ideas and culture of a given period. The value of classification, however, goes beyond a mere inven- tory or “table of contents,” no matter how complete. The very fact that classification appeals to logical criteria which may possibly be subjective or objective in nature gives us an initial idea of the obstacles con- fronting the classifier, difficulties scarcely encountered in the preparation of a catalogue, properly so called. Consequently, a well conducted effort at surveying the history of the classification of the sciences may be valuable in leading us to discover the connections and analogies existing among the different fields of knowl- edge at a given time, and within the context of a particular type of civilization. However, history of any sort is not a static phenomenon, but follows an evolu- tionary course. We are obliged therefore to study the sciences and their classification considered essentially as an historical process subject to continuous develop- ment. We shall thus see the appearance of the great currents of ideas which have sometimes dominated many centuries and we can seek what is less apparent, namely, the structure underlying these ideas.