78 THE PRINCIPLES OF SCIENCE. 



we might inadvertently but fallaciously infer that, Fixed 

 stars are not subject to gravity. To reduce the premises 

 to symbolic form, let 



A = planet 



B = fixed star 



C = subject to gravity ; 

 then we have the propositions 



A = AC (i) 



B = Ba. (2) 



The reader will try in vain to produce from these 

 premises by legitimate substitution any relation between 

 B and C ; he could not then commit the fallacy of 

 asserting that B is not C. 



There remain two other kinds of paralogism, com 

 monly known as the fallacy of Four Terms and the Illicit 

 Process of the Minor term. They are so evidently impos 

 sible while we obey the rule of the substitution of equi 

 valents, that it is not necessary to give any illustrations. 

 When there are four distinct terms in two propositions 

 there could be no opening for a substitution. As to the 

 Illicit Process of the Minor it consists in a flagrant sub 

 stitution for a term of another wider term which is not 

 known to be equivalent to it, and which is therefore 

 forbidden by our rule to be substituted for it. 



