DIVISION AND CLASSIFICATION. 133 



the thing defined (31, 32, 57, 67), we should imagine that such a combina 

 tion of genus and differentia would give us a logical definition of each such 

 sub-class ; and so it would, were the classifications in question regarded as 

 &quot; natural &quot;. But we are warned not to imagine that the &quot; modern zoologist 

 consciously and avowedly makes his scheme of classification a genealogical 

 [i.e. what he would regard as a * natural ] one &quot; ; * and &quot; in Systematic 

 Botany we are expressly reminded that [the * differentiating attribute] has no 

 significance, that whatever may be its apparent meaning or its actual 

 etymology we are to regard it as a mere unmeaning label. Thus perennis 

 as an adjunct [in * Bellis perennis ] does not mean that the daisy in question 

 lives for several years.&quot; 2 Both botanists and zoologists have presumably been 

 content to fix on qualifying titles which either indicate some prominent feature 

 of the sub-class, 3 or are connected with some other easily remembered fact j 

 they have not endeavoured in all cases to get names expressive of the &quot; natural &quot; 

 differentia of the sub-class. The result is that the sum of all the differentiae 

 leading from a summum genus to a lowest sub-class would give, not a 

 definition of the latter, but rather a sort of description, since &quot; we can hardly 

 consider that the meaning of the term could be stretched so as to include all 

 these attributes &quot; ; the latter constituting &quot; a curiously heterogeneous 

 group . . . some . . . really important in themselves . . . others . . . 

 very superficial &quot;. 4 



(ii) A second method of establishing a nomenclature express 

 ive of the mutual relations of the sub-classes, is the method 

 illustrated in the science of chemistry. Here the relations are 

 expressed by changes in the termination of the words. &quot; Thus the 

 new chemical school spoke of sulphuric and sulphurous acids ; of 

 sulphates and sulphites of bases ; and of sulphurets of metals ; 

 and in like manner, of phosphoric and phosphorous acids, 

 of phosphates, phosphites and phosphurets &quot; ; 5 of oxides and 

 hydrates, etc. &quot; In this manner a nomenclature was produced, 

 in which the very name of a substance indicated at once its con 

 stitution and place in the system.&quot; 6 



() It is no less essential to have a language in which to 

 describe objects, than to have names for the classes to which they 

 belong. This descriptive language is called Terminology. The 

 terms used are all general terms ; and they are combined to de 

 scribe the individual, its parts, and its properties. In the use of 

 such technical terms, accuracy and precision are of the greatest 



1 VENN, op. cit., p. 340. 2 ibid., p. 336. 



:t Constituting a &quot;diagnostic&quot; definition. Cf. supra, 65; JOSEPH, op. cit., p. 

 116. 



4 VENN, ibid., p. 326. 



SWHEWELL, Novum Organon Renovatnm, p. 308; apud WELTON, Logic, I, 

 pp. 148-9. 



ibid. 



