332 , PERSONAL PREPARATION FOR RESEARCH. 



machine,' for comparing ideas and ascertaining their 

 agreement or difference* of meaning by purely mechanical 

 means, or performing the mental process of judgment. 



CHAPTER XXXVI. 



USE OF THE REASONING POWER IN SCIENTIFIC RESEARCH. 



Within the "brain's most secret cells 



A certain Lord Chief Justice dwells 



Of sovereign power, whom one and all, 



With common voice, we Reason call. CHURCHILL. 



1 Reason is that faculty which, by comparing together two 

 propositions bearing a certain relation to each other, becomes 

 cognisant of a third proposition.' l 



THERE is no qualification in the art of scientific discovery 

 of equal importance to the power of reasoning correctly, 

 because reason is the chief faculty by means of which we 

 discern truth and ascertain the causes and explanations of 

 phenomena. Reasoning is the process by means of which 

 from certain propositions known or assumed, certain other 

 propositions, termed conclusions, follow as a matter of ne- 

 cessity ; and they necessarily follow because the original 

 propositions include them. An indispensable condition of 

 reasoning is mental consistency, i.e., consistency with our 

 previous assertions ; as all truth is universally consistent, 

 so should all thought be. If we admit a name, we must 

 also admit its synonym and all that it includes. If we 

 agree to a statement or reason, we must be prepared to 



1 W. G. Davies, ' On Mental Suggestion,' c., Psychological Journal^ 

 1862, p. 649. 



