CAUSE AND EFFECT— PROBABILITY 121 



ing how a particle of earth and a particle of sun move in 

 each other's presence. The description of that motion is 

 given by Newton's law of gravitation, but the wJiy of that 

 motion is just as mysterious to us as the motion of the 

 sun to the barbarian.^ No one knows why two ultimate 

 particles influence each other's motion. Even if gravita- 

 tion be analysed and described by the motion of some 

 simpler particle or ether-element, the whole will still be a 

 description, and not an explanation, of motion. Science 

 would still have to content itself with recording the Jtow. 

 In what we have termed secondary causes, therefore, 

 science finds no element of enforcement, solely the routine 

 of experience. But the idea of will as a first cause has 

 been over and over again associated with secondary 

 causes. Aristotle, noting the difficulty of explaining why 

 motions take place, introduced not only God as a first 

 cause, but, like primitive man, made God an immediate 

 source of the enforcement in every secondary cause. 

 God, Aristotle held, is continually imparting motion to 

 all the bodies in the universe, and so producing pheno- 

 mena. Aristotle's doctrine was accepted by the mediaeval 

 schoolmen, and for many centuries remained fundamental 

 in philosophical and theological writings. Schopenhauer, 

 the German metaphysician, perceiving that the only known 

 apparent first cause of motion was will, placed will behind 

 all the phenomena of the universe, much like the barbarian 

 who postulates the will of a storm-god behind the storm.^ 

 But however little logical basis these metaphysical specu- 



1 The reader will find it profitable to analyse what is meant l>y such state- 

 ments as that the law of gravitation causes bodies to fall to the earth. This 

 law really describes how bodies do fall according to our past experience. It 

 tells us that a body at the surface of the earth falls about sixteen feet towards 

 the earth in the first second, and at the distance of the moon about -jtVtt P^^t 

 of this distance in the same time. The law of gravitation describes the rate 

 at which a body falls, or, better, the rate at which its motion is changed at 

 diverse distances, and the force of gravitation is really a certain measure of 

 this change of motion, and no useful purpose can be served by defining it as 

 the cause of change in motion. Other physical laws ought to be interpreted 

 in the same anti-metaphysical manner. 



- Sir John Herschel went so far as to identify gravitation and will ! 

 {Outlines of Astronomy, arts. 439-40). Other samples of the same animistic 

 tendency will be found in the writings of Dr. J. Martineau anil the late Dr. 

 W. B. Carpenter. 



