122 MYSTICISM AND LOGIC 



not parts of the external world with which physics deals 

 Similar remarks will apply to the word &quot; independent.&quot; 

 Most of the associations of this word are bound up with 

 ideas as to causation which it is not now possible to 

 maintain. A is independent of B when B is not an 

 indispensable part of the cause of A. But when it is 

 recognised that causation is nothing more than correla 

 tion, and that there are correlations of simultaneity as 

 well as of succession, it becomes evident that there is 

 no uniqueness in a series of casual antecedents of a given 

 event, but that, at any point where there is a correlation 

 of simultaneity, we can pass from one line of antecedents 

 to another in order to obtain a new series of causal 

 antecedents. It will be necessary to specify the causal 

 law according to which the antecedents are to be con 

 sidered. I received a letter the other day from a corre 

 spondent who had been puzzled by various philosophical 

 questions. After enumerating them he says : &quot; These 

 questions led me from Bonn to Strassburg, where I found 

 Professor Simmel.&quot; Now, it would be absurd to deny 

 that these questions caused his body to move from 

 Bonn to Strassburg, and yet it must be supposed that a 

 set of purely mechanical antecedents could also be found 

 which would account for this transfer of matter from one 

 place to another. Owing to this plurality of causal series 

 antecedent to a given event, the notion of the cause 

 becomes indefinite, and the question of independence 

 becomes correspondingly ambiguous. Thus, instead of 

 asking simply whether A is independent of B, we ought 

 to ask whether there is a series determined by such and 

 such causal laws leading from B to A. This point is 

 important in connexion with the particular question 

 of objects of perception. It may be that no objects quite 

 like those which we perceive ever exist unperceived ; 



