METHODS OF PHYSIOLOGICAL RESEARCH 37 



it involves a complexity of sensations, my own idea, I must assume 

 that a reason for this idea exists. Hence the question arises, What 

 is the thing outside of my mind that produces in me through the 

 senses this idea ? In other words, what is the external world ? 



This question contains an error. As is well known, natural 

 science has shown that every phenomenon in the physical 

 world has as its cause another physical phenomenon. This is only 

 an expression of the law of cause and effect, 'i.e., the law of 

 causality. Hence the cause of my sensation of the physical is 

 another sensation or idea, which is located not outside of but 

 within my mind. This is nothing but a paraphrase for the fact 

 that our conception of causality has arisen out of a combination of 

 separate experiences, which our mind has obtained by observation 

 of the regular sequence of its own elements, its sensations and 

 ideas. In other words, causality itself, like all other sensations, 

 ideas, conceptions, or whatever we may term it, exists only in our 

 own mind. If, therefore, the cause of my idea of the physical is 

 located within, the supposition of a reality without is wholly un- 

 justified. 



Various philosophers have, in fact, endeavoured to base the reality 

 of an external world upon the causality of phenomena. But both 

 rest upon the same error, and the argument presents the rare 

 spectacle of an attempted proof of something by means of that 

 which is to be proved. 



It is not to be denied that to every one who follows this line of 

 thought for the first time the above result must appear paradoxical, 

 and he will immediately raise the objection that besides himself 

 many other men exist, possessing minds and capable of making 

 exactly the same assertions concerning themselves and their own 

 minds. But here the delusion is again evident. To me, other 

 men are bodies, I perceive in them nothing else. Hence they are 

 only my idea. And when they tell me that they have a mind like 

 myself, that they likewise feel and think, it is true ; but what they 

 say to me, their speech, their movements, are only physical 

 phenomena and, therefore, only my own ideas According to our 

 scientific mode of expression, their mind has its seat in their brain, 

 but if, by a surgical operation upon a living man, I am ever 

 enabled to examine the brain, I learn that nothing is to be found 

 there but physical elements. I am thus forced to the conclusion 

 that what I regard as the mind of another is also only my own 

 idea. In short, whatever path I take, I come constantly to the 

 conclusion that all that seems to be outside of me, whether it be 

 a lifeless body, a living man or a human mind, is in reality only 

 my own mind. Beyond my own mind I cannot go. My own 

 individuality, indeed, is only an idea of my mind, and, therefore, 

 I cannot finally say, the world is my idea, but I must say the 

 world is an idea, or a sum of ideas, and what appears to me as my 



