iv.] DEDUCTIVE REASONING. 61 



is abridged in common language by the ellipsis of the 

 circumstances which are not of immediate importance. 



Instead of all the propositions being exactly of the same 

 kind as in the last example, we may have a series of 

 premises of various character ; for instance, 



Common salt is sodium chloride, (i) 



Sodium chloride crystallizes in a cubical form, (2) 

 What crystallizes in a cubical form does not 



possess the power of double refraction ; (3 

 it will follow that 



Common salt does not possess the power of double 



refraction. (4) 



Taking our letter-terms thus, 

 A = Common salt, 

 B = Sodium chloride, 

 C = Crystallizing in a cubical form, 

 D = Possessing the power of double refraction, 

 we may state the premises in the forms 



A = B, (I) 



B = BC, (2) 



C = Cd. (3) 



Substituting by (3) in (2) and then by (2) as thus altered 

 in (i) we obtain 



A - BCrf, (4) 



which is a more precise version of the common conclusion. 

 We often meet with a series of propositions describing 

 the qualities or circumstances of the one same thing, and 

 we may combine them all into one proposition by the 

 process of substitution. This case is, in fact, that which 

 Dr. Thomson has called " Immediate Inference by the 

 sum of several predicates," and his example will serve my 

 purpose well. 1 He describes copper as "A metal of a 

 red colour and disagreeable smell and taste all the 

 preparations of which are poisonous which is highly 

 malleable ductile and tenacious with a specific gravity 

 of about 8.83." If we assign the letter A to copper, and the 

 succeeding letters of the alphabet in succession to the series 

 of predicates, we have nine distinct statements, of the form 



A = AB (i) A = AC (2) A = AD (3) A = AK (9). 



We can readily combine these propositions into one by 



1 An Outline of the Necesmry Lawt of Thvanht, Fifth Ed. p. 161. 



