500 LOGIC OF THE MORAL SCIENCES. 



the successions and coexistences of the mental states 

 of which they are supposed to be the generators or 

 causes. The successions, therefore, which obtain 

 among mental phenomena, do not admit of being 

 deduced from the physiological laws of our nervous 

 organization ; and all real knowledge of them must 

 continue, for a long time at least if not for ever,, to be 

 sought in the direct study, by observation and experi- 

 ment, of the mental successions themselves. Since 

 therefore the order of our mental phenomena must be 

 studied in those phenomena, and not inferred from the 

 laws of any phenomena more general, there is a dis- 

 tinct and separate Science of Mind. The relations, 

 indeed, of that science to the Science of Physiology 

 must never be overlooked or undervalued. It must by 

 no means be forgotten that the laws of mind may be 

 derivative laws resulting from laws of animal life, and 

 that their truth therefore may ultimately depend upon 

 physical conditions ; and the influence of physiological 

 states or physiological changes in altering or counter- 

 acting the mental successions, is one of the most 

 important departments of psychological study. 



3. The subject, then, of Psychology, is the uni- 

 formities of succession, the laws, whether ultimate or 

 derivative ,, according to which one mental state suc- 

 ceeds another ; is caused by, or at the least, is caused 

 to follow, another. Of these laws, some are general, 

 others more special. The following are examples of 

 the most general laws. 



First: Whenever any state of consciousness has 

 once been excited in us, no matter by what cause ; an 

 inferior degree of the same state of consciousness, a 

 state of consciousness resembling the former but 

 inferior in intensity, is capable of being reproduced in 



