SCIENTIFIC METHOD IN PHILOSOPHY 105 



has become more and more evident with the progress of 

 physics that large generaHsations, such as the conserva- 

 tion of energy or mass, are far from certain and are 

 very likely only approximate. Mass, which used to be 

 regarded as the most indubitable of physical quantities, 

 is now generally believed to vary according to velocity, 

 and to be, in fact, a vector quantity which at a 

 given moment is different in different directions. The 

 detailed conclusions deduced from the supposed constancy 

 of mass for such motions as used to be studied 

 in physics will remain very nearly exact, and therefore 

 over the field of the older investigations very little modi- 

 fication of the older results is required. But as soon as 

 such a principle as the conservation of mass or of energy 

 is erected into a universal a priori law, the slightest 

 failure in absolute exactness is fatal, and the whole 

 philosophic structure raised upon this foundation is 

 necessarily ruined. The prudent philosopher, there- 

 fore, though he may with advantage study the 

 methods of physics, will be very chary of basing 

 anything upon what happen at the moment to be 

 the most general results apparently obtained by those 

 methods. 



(2) The philosophy of evolution, which was to be our 

 second example, illustrates the same tendency to hasty 

 generalisation, and also another sort, namely, the undue 

 preoccupation with ethical notions. There are two 

 kinds of evolutionist philosophy, of which both Hegel 

 and Spencer represent the older and less radical kind, 

 while Pragmatism and Bergson represent the more 

 modem and revolutionary variety. But both these sorts 

 of evolutionism have in common the emphasis on progress, 

 that is, upon a continual change from the worse to the 

 better, or from the simpler to the more complex. It 



