This does not mean that it can now be left to one side; but that a reﬂection upon the history of a particular branch of knowledge can no longer content itself with following the development of that body of knowledge in a temporal sequence; such a body of knowledge is not, in fact, a phenomenon of heredity and tradition; and one does not explain how it came about simply by describing the state of knowledge that preceded it and what it has provided by way of as we say 'original contributions'.