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. 



