PROPOSITIONS. 49 



article a often seems to express partiality, as when we say 

 * Iron is a metal ' we clearly mean one only of several 

 metals. 



Certain eminent recent logicians have proposed to avoid 

 the indefiniteness in question by w^hat is called the Quan- 

 tification of the Predicate, and they have generally used 

 the little word some to show that only a part of the 

 predicate is identical with the subject . Some is an in- 

 determinate. adjective; it implies unknown qualities by 

 which we might select the part in question if they were 

 known, but it gives no hint as to their nature. I might 

 make extensive use of such an indeterminate sign to 

 express partial identities in this work. Thus, taking the 

 special symbol V = some, the general form of a partial 

 identity would be A = VB, and in Boole's Logic expres- 

 sions of the kind were freely used. But I find that 

 indeterminate symbols only introduce complexity, and 

 destroy the beauty and simple universality of the system 

 which may be created without their use. A vague word 

 like some is only used in ordinary language by ellipsis, 

 and to avoid the trouble of attaining accuracy. We can 

 always substitute for it more definite expressions if we 

 like ; but when once the indefinite some is introduced we 

 cannot replace it by the special description. We do not 

 know whether some colour is red, yellow, blue, or what it 

 is ; but on the other hand red colour is certainly some 

 colour ; as is also yellow, blue, &c. 



Throughout this system of logic I shall usually dispense 

 with all such indefinite expressions ; and this can readily 

 be done by substituting one of the other terms. To 

 express the proposition * All As are some BV I shall not 

 use the form A = VB, but 



c 'Elementary Lessons in Logic/p. 183. ' Substitution of Similars/ 



p. 7. 



E 



