288 ELEMENTS OF SCIENCE 



&c., but it may be equally a species, with respect to the 

 concept and name " European." 



Thus let the circle A (Fig. 54) represent the genus 

 "Jew," and B the differentiating quality "man of 

 Middlesex," then these by their intersection will con- 

 stitute C i.e., the species " Jew of Middlesex." 



On the other hand, A may represent the genus " man 

 of Middlesex," and B the quality " Jew," with the same 

 result with respect to C. Thus the genus and the 

 differential quality or " difference " may change places. 



Again B may be the genus u man," and A the quality 

 FIG. 54. 



B 



" hereditary observer of the Mosaic Law," when C will 

 be " Jew" as a species. 



A logical definition of any concept is formed by 

 uniting the proximate, or lowest, genus in which it 

 is contained, with its differential quality. 



The lowest species can never be a genus, and consists 

 only of the individuals which compose it. Similarly the 

 highest genus can never be a species because, being the 

 highest, it cannot be included, as a subordinate group, 

 within any higher one. 



Between the highest genus and the lowest species are 

 a multitude of genera which are called subalternate, 



