It is true that in order to obviate the evil of confusion and the defective consciousness of the various kinds of research which have been mingled together, many authors are in the habit of prefixing to their books theoretic introductions, about the _method,_ as they call it, of their science. The special logic of the individual disciplines is to be sought (they say) in the books that treat of these. Manuals in the German language are especially notable for this arrangement, preceded, as they are, by the heaviest introductions, which occupy a great part of the volume or of the volumes of the book. They present a contrast to French and English books, which usually enter at once _in medias res._ This arrangement seems preferable: the German type has against it the sensible observation of Manzoni, that one book at a time is enough, when it is not more than enough. He who opens a historical book in order there to learn the particulars of an event, or a book on economics in order to learn how an economic institution works, should not be obliged to read the theory of historica events and disquisitions on the place of Economics in the system of the sciences. _"Il s'agit d'un chapon et non point d'Aristote,"_ as the judge in the _Plaideurs_ said to the advocate who went back in his speech to the _Politics_ of Aristotle. But, besides the literary contamination, there is also here the other inconvenience, that science and the theory of the sciences being different operations and demanding different aptitudes and preparations, the specialist who is competent in the first is usually not at all competent in the second; though he may be believed to be so, owing to a confusion of names. Why, indeed, should an expert on banking and Stock Exchange business be versed in the gnoseology of economic science? The affirmation of competence in the one on the strength of competence in the other constitutes a true and proper sophism _a dicto simpliciter ad dictum secundum quid._ [Sidenote: _The capricious multiplication of the sciences._]