MOTION, FORCE, MATTER 329 



discussion, is motion; since particles exhibit motion and rest 

 they also exhibit changes of motion, and hence any other 

 property intimately connected with this phenomenon. 



The second refinement concerns the elimination of the 

 notion of compulsion which plays so prominent a part in the 

 first law. As has already been shown, there is some doubt 

 whether even at the empirical level the notion of causation 

 or necessity is an essential part of every force-experience. 

 The whole question is tied up with the idea that force in- 

 volves muscular action, and that changes in nature are 

 analogous to those found in acts of will. That this notion 

 played a prominent part in the thinking of primitive man 

 seems unquestionable, but that it should be eliminated so 

 far as possible from scientific thinking seems equally certain. 

 "The idea ... of enforcement, of some necessity in the 

 order of sequence, remains deeply rooted in men's minds, as 

 a fossil from the spiritualistic explanation which sees in will 

 the cause of motion. This idea is unfortunately preserved 

 in association with the scientific description of motion, and 

 in the materialist's notion of force as that which necessitates 

 certain changes or sequences of motion, we have a ghost of 

 the old spiritualism. . . . The necessity in a law of nature 

 has not the logical must of a geometrical theorem, nor the 

 categorical must of a human law-giver; it is merely our 

 experience of a routine, whose stages have neither logical 

 nor volitional order." x Furthermore, "though there is no 

 sense in saying that anthropomorphism is wrong," since 

 "we can never get away from it in at least a diluted form," 

 nevertheless this conception of force "is of doubtful value 

 for mechanics." 2 Recognizing, therefore, the necessity for 

 eliminating the notion of compulsion from Newton's first 

 law, one may restate it in such a way as to avoid this feature, 

 and to indicate more clearly that the law states merely a 

 correlation between force and change of motion. 'Every 

 particle in a state of change of motion (i.e., neither at rest, 



1 K. Pearson, Grammar of Science, pp. 119-120. 



2 R. B. Lindsay and H. Margenau, Foundations of Physics, p. 87. 



