Mental action depends upon change. 97 



viewed as a mode of energy ; it is essentially dy- 

 namic ; activity or change, within or without us, 

 appears to be the original source of all our mental 

 impressions, and the cause of their re-excitement in 

 an act of memory. A man's mind, being continually^, 

 excited by circumstances, must be active whether he ^ 

 will or no, and if it does not possess sufficient truthful 

 / ideas entirely to occupy it, it must be more or less 

 occupied with erroneous ones. " We can neither feel, 

 nor know, without a transition or change of state 

 and every cognition, must be viewed as in relation to 

 some other feeling, or cognition," (Bain. Mental and 

 Moral Science, p. 83); i.e. the mental effect of impres- 

 sions upon us depends upon our immediately previous 

 mental state ; consciousness and perception appear to 

 be based upon cerebral change or activity ; after 

 strong excitement of consciousness an increased 

 amount of acid products is found in the secretions. 

 " It is a general law of the mental constitution, more 

 or less recognised by inquirers into the human mind, 

 that change of impression is essential to consciousness 

 in every form," (Bain. Emotions and Will, 3rd edi. 

 p. 550). A sufficient degree also of such change is a 

 necessary condition of conscious perception ; it is the 

 stronger or more rapid only of mental changes that 

 excite our consciousness. 



We perceive nearly all things by means of a dif- 

 ference of impression which they make upon us ; by 

 contrast. That which makes no such difference of 

 impression, such as the great uniformities of time and / 



