2 COMPONENTS OF A CAUSAL EXPLANATION OF BRADFORD LAW

One can suppose that Bradford's law is valid for all scientific fields . As an implication of this general validity and because of limitation s of space, journals must differ in their subject structure, and every journal must have its own hierarchy of subjects, conforming to a Brad ford or a similar distribution. The phenomenon of subject hierarchies is shown here for ten journals in twentieth-century psychology and mat hematical logic and for five journals in nineteenth-century mathematic s, taking instead of Bradford's original rank-size distribution the eq uivalent, but more general, Pareto distribution. It is hypothesised th en that hierarchies of subjects within journals correspond to the rece ption process, i.e. to the structure of interests of their readers. Th is is illustrated by means of an example of 30 most prolific nineteent h-century mathematicians. It is argued that the phenomenon of subject hierarchies in journals and in readers has to be considered in a causa l explanation of Bradford's law.