90 DOGMATISM AND EVOLUTION 



accordance with change in their relations. That is to say, the 

 relativity is not simply mathematical, but also dynamical. Fur- 

 thermore, in the dynamical as well as in the mathematical sense 

 of the term, the relativity is not to a few things, or even to things 

 in general, but to the universe as a system of interrelated things. 

 This is the principle of universal reciprocal determination, for 

 which Newton gave a solid basis by his discovery of the law of 

 gravitation, and which Leibniz proclaimed, while he yet denied 

 it, in his theory of the preestablished harmony. 



If then the distinction between the essential and the relative 

 was anywhere to be made out, it would have to be in the case of 

 thinking substances, or souls. But, in the first place, where a 

 distinct class of such substances was recognized, they had always 

 been treated after the analogy of material substances. This was, 

 of course, unavoidably true, where the characteristics of the soul- 

 substance were simply the negatives of those of all (or some) 

 material things : simple, incorruptible, immortal, etc. But it was 

 also true of its own peculiar attribute of thinking, which was 

 always thought of in express opposition to the material attribute 

 of extension. A changed interpretation of the latter was therefore 

 bound in some measure to affect the former. In the second place, 

 a line of argument precisely similar to that which had transformed 

 the material attributes into relations was readily applicable to the 

 qualities and functions of the soul. Whether the essence of the 

 soul was (with Descartes) to think, or (with Leibniz) the energy 

 by which its ideas, conscious or unconscious, are determined, it 

 was necessary that this essence be inseparable from the soul- 

 substance, and, independently of everything else, equally char- 

 acterize it at all times. But so far as unprejudiced observation 

 could show, the soul's faculty of thought or ideation is quite as 

 relative to circumstances as the color or density of matter. To 



be said to be a name for the fact, that a given force, acting upon different bodies, 

 produces in a given time accelerations that vary only from body to body. Now 

 since a force acting upon one body is always a strain between two, it is obvious 

 that mass does not belong to any particular body apart from its dynamic relations 

 to other bodies. 



