EMANCIPATION FROM SCIENTIFIC MATERIALISM. 431 



of thought which we have constructed for ourselves (rather 

 imperfectly) in order to express that which is lasting in the 

 changeableness of phenomena. Now that we begin to 

 grasp that the Actual, i.e., that which acts upon us, is energy 

 alone, we must inquire in what relation the two conceptions 

 stand to one another, and the result is undoubtedly that 

 the predicate of reality can be affirmed of Energy only. 



This decisive aspect of the new conception will perhaps 

 stand out more clearly if I sketch the development of the 

 idea in question in a short historical resume. We have 

 already seen that progress in science is characterised by the 

 discovery of ever more general invariants, and I have also 

 indicated how the first of these invariable quantities, mass, 

 was extended to matter, i.e., mass accompanied by volume, 

 weight, and chemical properties. This conception was, 

 however, obviously insufficient to embrace phenomena in 

 their continual changeableness, and from Galileo's time on- 

 wards the idea of force has been added in order to suit 

 this phase of nature. But force lacked the property of 

 constancy, and after vis viva and work had been found to 

 be mechanical functions exhibiting the properties of partial 

 invariants, Mayer discovered in energy the most general 

 invariant which rules the whole dominion of physical 

 forces. 



In accordance with this historical development, matter 

 and energy continued to exist side by side, and all that 

 could be said about their mutual relation was that they 

 occurred for the most part together or that matter was the 

 carrier or holder of energy. 



But are matter and energy things essentially different 

 from one another, as perhaps Body and Soul ? Or is not 

 rather all that we know and say of matter already contained 

 in the idea of energy, so that we can represent with this 

 latter quantity the totality of phenomena? According to 

 my conviction there can be no doubt as to the answer. 

 Hidden in the conception of matter are the following ideas : 

 first of all, mass, that is, the capacity factor of kinetic 

 energy ; further, the occupation of space or volume energy ; 

 again, weight or that particular kind of distance energy 



