CLASSIFICATION. 375 



his books on Physics, into those which treat of Mechanical 

 Motion, those which treat of Heat, those which treat of Light, 

 of Electricity, of Magnetism. 



Between these two modes of classification note the essential 

 distinctions. Arrangement according to any single con 

 spicuous attribute is comparatively easy, and is the first that 

 suggests itself : a child may place books in the order of their 

 sizes, or according to the styles of their bindings. But ar 

 rangement according to combinations of attributes which, 

 though fundamental, are not conspicuous, requires analysis; 

 and docs not suggest itself till analysis has made some pro 

 gress. Even when aided by the information which the 

 author gives on his title page, it requires considerable know 

 ledge to classify rightly an essay on Polarization ; and in the 

 absence of a title page it requires much more knowledge. 

 Again, classification by a single attribute, which the objects 

 possess in different degrees, may be more or less serial, or 

 linear. Books may be put in the order of their dates, in 

 single file; or if they are grouped as works in one volume, 

 works in two volumes, works in three volumes, &c., the groups 

 may be placed in an ascending succession. But groups 

 severally formed of things distinguished by some common 

 attribute which implies many other attributes, do not admit 

 of serial arrangement. You cannot rationally say either that 

 Historical Works should come before Biographical Works, or 

 Biographical Works before Historical Works ; nor of the sub 

 divisions of creative Literature, into Fiction, Poetry, and the 

 Drama, can you give a good reason why any one should take 

 precedence of the others. 



Hence this grouping of the like and separation of the un 

 like which constitutes Classification, can reach its complete 

 form only by slow steps. I have shown (Essays, Vol. II., pp. 

 145-7) that, other things equal, the relations among pheno 

 mena are recognized in the order of their conspicuousness ; 

 and that, other things equal, they are recognized in the order 

 of their simplicity. The first classifications are sure, there- 

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