74 THE PRINCIPLES OF SCIENCE. 



that which Archbishop 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 tena- 

 cious, 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 

 substituting for A in the second side of (i) its expression 

 in (2). We thus get 



A = ABC, 



and by repeating the process over and over again we 

 obtain the single proposition 



A = ABCDEFGHIJK. 



But Dr. Thomson is mistaken in supposing that we can 

 obtain in this manner a definition of copper. Strictly 

 speaking, the above proposition is only a description of 

 copper, and all the ordinary descriptions of substances 

 in scientific works may be summed up in this form. 

 Thus we may assert of the organic substances called 

 Paraffins that they are all saturated hydrocarbons, in- 

 capable of uniting with other substances, produced by 

 heating the alcoholic iodides with zinc, and so on. It 

 may be shown that no amount of ordinary description 

 can be equivalent to definition. 



Fallacies. 



I have hitherto been engaged in showing that all the 

 forms of reasoning of the old syllogistic logic, and an 

 indefinite number of other forms in addition, may be 

 i ' Au Outline of the Laws of Thought,' Fifth Ed. p. 161. 



