252 DOGMATISM AND EVOLUTION 



of a study of the ropes and wheels of common life; and, if they 

 are abstractions, it is because such abstractions are a practical 

 necessity and owe their justification to their necessity. More- 

 over, it is only by regarding the actual ropes and wheels as if 

 they were perfectly flexible and perfectly frictionless, that the prin- 

 ciple of the pulley can be applied to them. It is true that such 

 procedure involves error, for which allowance may be made. 

 But allowance is made only for error that is not negligible; and 

 it is made, too, in terms that are as ideal and schematic as the 

 perfect pulley itself; and when all is said and done there ever 

 remains uneliminated error, whose correction would demand an 

 infinite analysis. What the instrumentalist would point to as sig- 

 nificant is just this ever-present factor of negligible error. Just 

 what degree of error is negligible in a given case is always deter- 

 mined by the purpose for which the calculation is made. Whether 

 the actual structure of ropes and wheels and weights is a real 

 pulley or not depends on whether, for the needs of the existing 

 occasion, the cords and wheels may be regarded as if perfectly 

 flexible and perfectly frictionless. In short, the dispute as to 

 whether the pulley of abstract mechanics or the structure of ropes 

 and wheels which draws the bucket of water from the well is the 

 real pulley, is after all a verbal difference. The one is real, just 

 because of its practical usefulness in computations; the other is a 

 real pulley, because it may, for the purpose in hand, be regarded 

 as conforming to the conditions defined by mechanics. 



From the standpoint of instrumentalism, the case is similar as 

 regards reality and truth. It may be admitted that, abstractly 

 considered, we find a pure case of reality only in the completely 

 determined, the object of absolute knowledge. Shall we then 

 say that the things of human experience are merely phenomenal, 

 in that we know them as only partially determined, or even be- 

 cause it is evident that, were they known to us as completely 

 determined, they would thereby become transformed beyond 

 recognition? Shall we say that all human judgments are essen- 

 tially untrue, because their correction would involve an infinite 



