MOTION, FORCE, MATTER 327 



not causal connection but mere concomitance; force and 

 change of motion coexist in events of certain kinds, but no 

 invariable temporal relation and no relation of causal efficacy 

 seem to be indisputably present. Furthermore, concomitance 

 does not mean identity. Though force and motion are pre- 

 sumed to be coexistent features of certain events, they are 

 distinguishable. In this respect they are analogous to cer- 

 tain other sense qualities, e.g., spatial extent and color; all 

 extensions are colored and all colors are extended, yet one 

 has no difficulty distinguishing these qualities from one 

 another. Hence at the empirical level force is neither the 

 cause nor the effect of change of motion, nor is it to be 

 identified with change of motion; the two are simply con- 

 comitants. 



Finally, as in the case of motion, force is quantitative. 

 This is simply to say that forces may differ from one another 

 in a way which permits the observer to say that one is 

 greater in intensity than another. The force felt in bending 

 a bow is greater than that felt in stretching a small rubber 

 band, and the force imparted by a moving baseball is greater 

 than that imparted by a tennis ball moving with the same 

 velocity. Forces also exhibit differences in direction. A 

 force up differs from a force down, and a force to the left 

 from one to the right. 



force: scientific content 



As a first approximation to a scientific definition of force, 

 one may say that force means 'whatever is asserted about 

 force in any propositions of science in which the word or 

 symbol occurs. Whatever may be asserted as a true proposi- 

 tion about force says something about force, and the totality 

 of such assertions constitutes the meaning of the concept. 

 Furthermore, since the important statements about force 

 in science are mathematical, force may be defined as the 

 totality of mathematical equations in which / occurs. 



What is required in science, however, is not primarily a 

 knowledge of everything that may be said about force but 



