286 NATURE AND MAN. 



mental facts of consciousness on which Descartes himself built up 

 his philosophical fabric, dwelling exclusively on physical action as 

 the only thing with which science has to do, and repudiating the 

 doctrine (based on the universal experience of mankind) that the 

 mental states which we call volitions and emotions have a causative 

 relation to bodily changes, they appear to me to grasp only one 

 half of the problem, to see only one side of the shield. That the 

 principle of the conservation of energy holds good not less in the 

 living body than in the inorganic world, I was myself among the 

 earliest to maintain.* That in the most powerful muscular effort 

 which can be called forth by the human will, there is no more a 

 creation of energy than in an automatic convulsion, I believe as 

 firmly as Professor Clifford. And that the general tendency of 

 modern scientific research is to extend the domain of law to every 

 form of mundane change, — the belief in the uniformity of causation 

 being now assumed as axiomatic in all scientific procedure, — I 

 recognize as fully as Mr. Herbert Spencer. This tendency could 

 not be expressed more forcibly than in the following citation from 

 Mr. H. Sidgwick's recent treatise : — 



"The belief that events are determinately related to the state 

 " of things immediately preceding them, is now held by all com- 

 " petent thinkers in respect of all kinds of occurrences except human 

 " volitions. It has steadily grown both intensively and extensively, 

 " both in clearness and certainty of conviction, and in universality 

 " of application, as the human mind has developed and human 

 " experience has been systematized and enlarged. Step by step, in 

 "successive departments of fact, conflicting modes of thought 

 " have receded and faded, until at length they have vanished every- 

 " where, except from this mysterious citadel of will." f 



Before inquiring, however, whether there is adequate ground 

 for regarding the human will in this exceptional light, it may be 

 well to consider what basis there is for the assumption that the 

 range of physical causation extends itself from the sphere of matter 

 to that of mind, — in other words, that moral causation and physical 

 causation are convertible terms. 



* " On the Mutual Relations of the Vital and Physical Forces," Philosophical 

 Transactions, 1850. 



t " The Methods of Ethics," p. 47. 



