And this is just the occasion to make clear the distinction that we have on several occasions employed, between forms of knowledge and literary or didactic forms of knowledge, between the orders of knowledge and books. The arrangement of books is not always determined solely by the demand for the strict treatment of a determinate problem; very frequently, its motive is supplied by the practical need of having certain different pieces of knowledge collected together, in order not to be obliged to go and search for them in several places, that is to say, in their true places. Thus, side by side with scientific treatises properly so-called, are to be found scholastic compilations and manuals. Such are Geographies, Pedagogies, juridical or philological Encyclopædias, Natural Histories, and so on. Authors, even outside strictly scholastic limits, used formerly to consider it convenient sometimes to isolate, sometimes to unite certain orders of knowledge, and to baptize the mutilation or mixture with a particular name. It is evident that when dealing with these hybrid compilations and formations the philosopher and the historian of the sciences, who seek not books, but ideas, must carry out a series of analyses and syntheses, of disassociations and associations, without allowing themselves to be seduced by the authority of the writers or by the solidity of these mixtures, which have become traditional. [Sidenote: _Prejudices arising from these last._] But it is not an easy matter. Those mixtures are no longer ingenuous, nor are the practical motives that have determined them apparent. Around them has grown up a dense forest of philosophemes, of capricious distinctions, of false definitions, of imaginary sciences, of prejudices of every sort. Any one who has succeeded in discerning the genuine connections and attempts to separate the interlaced boughs, to isolate the trees and to show the different roots, any one who sets an axe to those wild tree-trunks, is horrified by cries and complaints, not less resonant than those that drove Tancred from the enchanted wood. And there is the traditionalist who admonishes us severely not to divide _natural_ groupings and not to introduce among them our own _caprice._ Thus he calls the capricious natural and the natural capricious. "What?" (has recently written the shocked Professor Wundt) "for the excellent reason that the search for the individual is historical search, must Geology be considered history and research relating to the glacial epoch be abandoned to the amiable interest of the historian?" And others lament that the ancient _richness_ of the sciences is destroyed by these simplifications, and call the confusion richness. [Sidenote: _Methodical prologues to Scholastic Manuals and their powerlessness._]