THE PRINCIPLES OF SCIENCE. [CHAP. 



The Powers of Mind concerned in the Creation of Science. 



It is no part of the purpose of this work to investigate the 

 nature of mind. People not uncommonly suppose that 

 logic is a branch of psychology, because reasoning is a 

 mental operation. On the same ground, however, we 

 might argue that all the sciences are branches of psy- 

 chology. As will be further explained, I adopt the opinion 

 of Mr. Herbert Spencer, that logic is really an objective 

 science, like mathematics or mechanics. Only in an in- 

 cidental manner, then, need I point out that the mental 

 powers employed in the acquisition of knowledge are prob- 

 ably three in number. They are substantially as Professor 

 Bain has stated them l : 



1. The Power of Discrimination. 



2. The Power of Detecting Identity. 



3. The Power of Eetention. 



We exert the first power in every act of perception. 

 Hardly can we have a sensation or feeling unless we dis- 

 criminate it from something else which preceded. Con- 

 sciousness would almost seem to consist in the break 

 between one state of mind and the next, just as an induced 

 current of electricity arises from the beginning or the 

 ending of the primary current. We are always engaged in 

 discrimination ; and the rudiment of thought which exists 

 in the lower animals probably consists in their power of 

 feeling difference and being agitated by it. 



Yet had we the power of discrimination only, Science 

 could not be created. To know that one feeling differs 

 from another gives purely negative information. It cannot 

 teach us what will happen. In such a state of intellect 

 each sensation would stand out distinct from every other ; 

 there would be no tie, no bridge of affinity between them. 

 We want a unifying power by which the present and the 

 future may be linked to the past ; and this seems to be 

 accomplished by a different power of mind. Lord Bacon 

 has pointed out that different men possess in very different 

 degrees the powers of discrimination and identification. It 

 may be said indeed that discrimination necessarily implies 

 the action of the opposite process of identification ; and so 

 1 The Senses and the Intellect, Second Ed., pp. 5, 325, &c. 



