532 LOGIC OF THE MORAL SCIENCES. 



of the mental successions themselves. Since therefore the order of our 

 mental phenomena must be studied in those phenomena, and not in- 

 ferred 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 un- 

 dervalued. It must by no means be forgotten that the law^s of mind 

 may be derivative laws resulting from laws of animal life, and that 

 their ti-uth, therefore, may ultimately depend upon physical conditions ; 

 and the influence of physiological states or physiological changes in 

 altering or counteracting the mental successions, is one of the most 

 important departments of psychological study. 



§ 3. The subject, then, of Psychology, is the uniformities of succes- 

 sion, the laws, whether ultimate or derivative, according to which one 

 mental state succeeds 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 us, without 

 the presence of any such cause as excited it at first. Thus, if we have 

 once seen or touched an object, we can afterwards think of the object 

 although it be absent from our sight or from our touch. If we have 

 been joyful or grieved at some event, we can think of, or remember, 

 our past joy or gi'ief, although no new event of a happy or a painful 

 nature has taken place. When a poet has put together a mental pic- 

 ture of an imaginary object, a Castle of Indolence, a Una, or a Juliet, 

 he can afterwards think of the ideal object he has created, without any 

 fresh act of intellectual combination. This law is expressed by saying, 

 in the language of Hume, that every mental impression has its idea. 



Secondly : These Ideas, or secondary mental states, are excited by 

 our impressions, or by other ideas, according to certain laws which 

 are called Laws of Association. Of these laws the first is, that simi- 

 lar ideas tend to excite one another. The second is, that when two 

 impressions have been frequently experienced (or even thought of) 

 either simultaneously or in immediate succession, then whenever 

 either of these impressions or the idea of it recurs, it tends to excite 

 the idea of the other. The third law is, that gi'eater intensity, in either 

 or both of the impressions, is equivalent, in rendering them excitable 

 by one another, to a greater frequency of conjunction. These are the 

 laws of Ideas : upon which I shall not enlarge in this place, but 

 refer the reader to works professedly psychological, in particular to 

 Mr. Mill's Analysis of the Phenomena of the Human Mind, where the 

 principal laws of association, both in themselves and in many of their 

 applications, are copiously exemplified, and with a masterly hand. 



These simple or elementary Laws of Mind have long been ascer- 

 tained by the ordinary methods of experimental inquiry ; nor could 

 they have been ascertained in any other manner. But a certain num- 

 ber of elementary laws having thus been obtained, it is a fair subject 

 of scientific inquiry how far those laws can be made to go in explain- 

 ing the actual phenomena. It is obvious that complex laws of thought 

 and feeling not only may, but must, be generated from these simple 



