MOTION, FORCE, MATTER 337 



The result of this rather disorganized discussion of the 

 concept of force is approximately as follows: Force at the 

 empirical level is a vague name for a great variety of data, 

 unquestionably present, yet incapable of precise char- 

 acterization; these data seem to be always associated with 

 events, often associated with motion, and capable of quan- 

 titative differentiation. Force at the scientific level is what 

 is obtained when the attempt is made to determine pre- 

 cisely where forces are, and how intense their manifestations 

 are, i.e., their loci and their measured values. But the at- 

 tempt to measure force reveals the fact that there is nothing 

 among the psychological simples of experience by which 

 this can be done. However, there is revealed a somewhat 

 obscure feature of nature, viz., a certain quotient of accelera- 

 tions, which seems to afford the required empirical basis; 

 this is called "mass," and is defined as proportionate to 

 force. Then force becomes measurable in terms of mass. This 

 makes mass psychologically derivative, but logically basic. 

 The operational derivation of the concept of force is therefore 

 simply the route by which its measured value is determined. 



matter: empirical foundation 



It is likely that the concept of matter is both the most 

 obscure of the basic physical concepts and the most ambig- 

 uous of philosophical notions. This is due partly to its long 

 and controversial history. But it is to be explained also by 

 the fact that the term "matter" has been employed to 

 designate features of nature which are widely different from 

 one another. An examination of the great variety of con- 

 texts in which the term has been used demonstrates this 

 ambiguity quite clearly. For example, " matter' : may be 

 used as synonymous with "thing," "body," or "substance," 

 to be contrasted with "property," "aspect," or "quality"; 

 or it may be used as equivalent to "particular," as opposed 

 to "universal"; or "content," as opposed to "form"; or 

 "physical," as opposed to "mental" or "spiritual"; or 

 "real," as opposed to "unreal" or "imaginary." It seems 



