50 THE PRINCIPLES OF SCIENCE. [CHAP. 



Immediate Inference. 



Probably the simplest of all forms of inference is that 

 which has been called Immediate Inference, because it can 

 be performed upon a single proposition. It consists in 

 joining an adjective, or other qualifying clause of the same 

 nature, to both sides of an identity, and asserting the 

 equivalence of the terms thus produced. For instance, 

 since 



Conductors of electricity = Non-electrics, 

 it follows that 



Liquid conductors of electricity = Liquid non-electrics. 

 If we suppose that 



Plants = Bodies decomposing carbonic acid, 

 it follows that 



Microscopic plants = Microscopic bodies decomposing 



carbonic acid. 

 In general terms, from the identity 



A = B 

 we can infer the identity 



AC = BC. 



This is but a case of plain substitution ; for by the first 

 Law of Thought it must be admitted that 



AC = AC, 



and if, in the second side of this identity, we substitute 

 for A its equivalent B, we obtain 

 AC = BC. 

 In like manner from the partial identity 



A = AB 

 we may obtain 



AC = ABO 



by an exactly similar act of substitution ; and in every 

 other case the rule will be found capable of verification by 

 the principle of inference. The process when performed as 

 here described wiU be quite free from the liability to error 

 which I have shown * to exist in " Immediate Inference by 

 added Determinants," as described by Dr. Thomson 2 



