136 INTRODUCTION TO PHILOSOPHY OF SCIENCE 



lead and iron, which present such conspicuous points of 

 similarity as regards density, metallic lustre, malleability, 

 etc." x 



It seems to be essential to the notion of classification as 

 employed in empirical science that its results are considered 

 merely as tentative. A property which appeared to be ob- 

 vious may prove to be somewhat obscure on more careful 

 examination; superficial resemblances may hide deeper dif- 

 ferences, and superficial differences may hide deeper re- 

 semblances. Jevons goes on to point out that the early 

 classification of metals is soon seen to exhibit difficulties. 

 "Antimony, bismuth, and arsenic are distinctly metallic as 

 regards lustre, density, and some chemical properties, but 

 are wanting in malleability. ... In this way it comes to 

 pass that almost every classification which is proposed in 

 the early stages of a science will be found to break down as 

 the deeper similarities of the objects come to be detected." 2 



The classificatory schemes found in such a science may be 

 called "diagnostic'' or 'indexical." They are essentially 

 practical in character and serve merely as techniques for 

 locating events conveniently. Their purpose is not to reveal 

 remote similarities or abstruse connections, but merely to 

 afford simple devices by which objects may be referred to 

 their proper classes, and other properties inferred. Often the 

 classificatory scheme is nothing more than an index or cat- 

 alogue by means of which one establishes a correlation 

 between a place where an object may be found and a certain 

 tag which is attached to the object, as in the case of a tele- 

 phone directory. Negatively, one may say that classificatory 

 schemes at this level of science do not exhibit hidden re- 

 semblances. For example, one would not expect to find 

 circles classified with rectilinear figures, though abstractly 

 they may be considered as rectilinear figures of an infinite 

 number of sides; nor would one expect chlorine which is a 

 gas, bromine which is a liquid, and iodine which is a solid 

 to be classified together in spite of their similarity in 



1 W. S. Jevons, Principles of Science, p. 690. 2 Ibid., p. 691. 



