368 ELEMENTS OF SCIENCE 



we had to prove the validity of that process, such a 

 proof would require a second proof, that again would 

 require a third, that third a fourth, and so on for ever. 

 In other words, there could be no such thing as proof 

 at all. 



Now no one who argues, or who listens to, or reads 

 (with any serious intention) the arguments of others, 

 can, without stultifying himself, profess to think that 

 no process of reasoning is valid. If the truth of no 

 mode of reasoning is certain, if we cannot draw any 

 certain inferences whatever, then all arguments must be 

 useless, and to proffer or consider them must be alike 

 vain. And not only must all reasoning addressed to 

 others be thus vain, but the silent reasonings of solitary 

 thought must also be vain. This is equivalent to 

 declaring all men to be idiots. But a man who honestly 

 considers all other men to be mad, is generally, and not 

 unreasonably, deemed to be somewhat intellectually 

 deficient himself. Thus the validity of the process of 

 reasoning can but depend upon its own evidence. It 

 depends on the clear and manifest evidence it possesses 

 for any one who will consider it and who understands 

 the meaning of the idea " therefore " when plainly 

 showing how one truth results from another how, e.g., 

 the mortality of Socrates is involved in the fact that 

 mortality is common to the whole human race. 



Thus the validity of the process of reasoning is evident 

 in itself ; but the truth of any particular inference 

 depends, and must depend, upon certain facts which are 

 known to us independently of and without reasoning. 

 We could not, for example, conclude that the fact of 

 some animal having a spinal column,* proved it to be a 



* See ante, p. 234. 



