332 PROF. W. STANLEY JEVONS ON 



Let the term_, when enclosed in brackets^ acquire a quan- 

 titative meaning, so as to denote the number of individuals 

 or objects which possess those qualities. Then 



(A) = number of objects possessing qualities of A, 

 or say, for the sake of brevity, the number of A^s. If, for 

 instance, 



A = character and quality of being a Member of Parlia- 

 ment, 



(A) =number of existing Members of Parliament = 658. 



5. Every logical proposition or equation now gives rise 

 to a corresponding numerical equation. Sameness of qua- 

 lities occasions sameness of numbers. Hence if 



A = B 



denotes the identity of the qualities of A and B, we may 



conclude that 



(A) = (B). 



It is evident that exactly those objects, and those objects 

 only, which are comprehended under A must be compre- 

 hended under B. It follows that wherever we can draw 

 an equation of qualities, we can draw a similar equation of 

 numbers. Thus, from 



A=B = C, 



we infer 



A=C; 



and similarly from 



(A) = (B)=(C), 



meaning the number of A^s and C^s are equal to the number 

 of B's, we can infer 



(A) = (C) 



But, curiously enough, this does not apply to negative 

 propositions and inequalities. For if 



A=B-D 



