xxx.] CLASSIFICATION. 677 



modify the above statement, as follows: "By the classifica- 

 tion of any series of objects, is meant the actual or ideal 

 arrangement together of those which are like and the separa- 

 tion of those which are unlike, the purpose of this arrange- 

 ment being, primarily, to disclose the correlations or laws of 

 union of properties and circumstances, and, secondarily, to 

 facilitate the operations of the mind in clearly conceiving 

 and retaining in the memory the characters of the objects 

 in question." 



Multiplicity of Modes of Classification. 



In approaching the question how any given group 

 of objects may be best classified, let it be remarked that 

 there must generally be an unlimited number of modes 

 of classifying a group of objects. Misled, as we shall see, 

 by the problem of classification in the natural sciences, 

 philosophers seem to think that in each subject there 

 must be one essentially natural system of classification 

 which is to be selected, to the exclusion of all others. 

 This erroneous notion probably arises also in part from the 

 limited powers of thought and the inconvenient mechani- 

 cal conditions under which we labour. If we arrange the 

 books in a library catalogue, we must arrange them in 

 some one order ; if we compose a treatise on mineralogy, 

 the minerals must be successively described in some one 

 arrangement ; if we treat such simple things as geometrical 

 figures, they must be taken in some fixed order. We shall 

 naturally select that arrangement which appears to be most 

 convenient and instructive for our principal purpose. But 

 it does not follow that this method of arrangement possesses 

 any exclusive excellence, and there will be usually many 

 other possible arrangements, each valuable in its own way. 

 A perfect intellect would not confine itself to one order of 

 thought, but would simultaneously regard a group of 

 objects as classified in all the ways of which they are 

 capable. Thus the elements may be classified according 

 to their atomicity into the groups of monads, dyads, triads, 

 tetrads, pentads, and hexads, and this is probably the most 

 instructive classification ; but it does not prevent us from 

 also classifying them according as they are metallic or non- 

 metallic, solid, liquid or gaseous at ordinary temperatures, 



