COMMON SENSE (aND SCIENCE ) 21 



seeks its own level becomes meaningful and useful only if I can 

 recognize "water" and the behavior known as "seeking its own level." 



How precise are these denotations? Their precision is the resultant 

 of a complex process in which desire for reliability and desire for 

 generality (and simplicity) pull in opposite directions. Guided by 

 our past experience we may elect to spell out the denotations in 

 such detail that the risk of misunderstanding is minimized. But by 

 that very act we also minimize the concepts' applicability: the things 

 and situations of the present (and future) will never precisely repro- 

 duce those of the past. The whole possibility of achieving a generally 

 useful colligative relation thus hinges on our willingness not to 

 specify too rigidly the denotations of its conceptual terms. 



What do I take to be the denotation of "water"? Sometimes clear, 

 sometimes turbid; sometimes "hard," sometimes "soft"; limpid or 

 colored; bland, salty, or bitter; warm or cold; odorless or pungent; 

 potable or contaminated; liquid, solid, or gaseous— how equivocal 

 can a specification be? Yet men of common sense ordinarily agree 

 on what is to be classified as "water." As already noted, the existence 

 of a purpose for which the classification is made sharpens discrim- 

 ination: it establishes the crucial functional characteristics for all 

 who share that purpose. In any matter of seeking its own level, 

 "water" need only be a uniformly dense liquid of modest viscosity- 

 nothing else "counts." For thirsty travelers in the Mohave desert a 

 particular solid will be happily accepted as "water"; but for the cap- 

 tain of a Greenland patrol ship a large block of that particular solid 

 is not "water" but "menace." The concept remains broadly applicable 

 because its denotation rests imprecise, sharpened only as required by 

 the "common sense" of those who, for one purpose or another, must 

 deal with "water." 



In common sense the tension between the desire for precision and 

 the desire for generality is most often resolved in favor of generality. 

 The number of concepts and relations -with which common sense can 

 work ejffectively is, we shall find, severely restricted. Each concept, 

 each relation, must then render maximum service; and a good deal 

 will be sacrificed in the way of reliability to obtain maximum gen- 

 erality. We all share Poincare's feeling that: "It is far better to fore- 

 see even without certainty than not to foresee at all." Moreover, in 

 the aflFairs of everyday life, with which common sense must deal, we 

 constantly meet multiple special contingencies that no colligative 



