THE PRINCIPLES OF SCIENCE 213 



Thus dependent on the accreditation of human scientists humanly 

 falHble, is the distinction of primary and secondary quahties any- 

 thing more than a convention? 



Observe the change of classification with time. For Aristotle hot- 

 ness, coldness, wetness, and dryness were the primary qualities, and 

 this we deny. For Newton hardness was a primary quality, which 

 we deny, and the "charge" we regard as primary could not so be 

 regarded by Newton. At any one time the adoption of a single clas- 

 sification is essential: only so can the scientific endeavors of an age 

 gain coherence and mutual relevance. Our present classification 

 seems well justified by notable successes won with it in the past. 

 But if future efiForts fail to yield equally notable finds then, if only 

 after prolonged struggle, we will again learn a new and better 

 classification. 



The distinction of primary and secondary qualities focuses atten- 

 tion on certain types of explanatory endeavors earlier found fruitful, 

 and correspondingly diverts attention from others earlier found un- 

 rewarding. In this last function the distinction is affiliated with a 

 large group of inhibitory principles, all having the form: "Thou 

 shalt not waste thy powers in vain endeavors." What endeavors are 

 considered "vain" will vary with the development of science. Late 

 in the 18di century the French Academy announced that it would no 

 longer consider papers on perpetual-motion machines. Essentially 

 this made official a judgment that attempts to devise such machines 

 are vain endeavors, and we have not since found occasion to revise 

 this judgment. On the other hand, the transmutation of the elements 

 that most responsible 19th-century scientists regarded as wholly vain 

 —and quite rightly so, considering the means at their disposal— has 

 been achieved in the 20th century. 



An inhibitory principle is a warning posted at the edge of an abyss 

 presently unfathomable. Some such principles {e.g., that rejecting 

 the possibility of perpetual-motion rfiachines ) are justified by a long 

 antecedent history of failure; others are justified on the warranty of 

 apparently indubitable theories. By curbing endeavors all too prob- 

 ably vain in the contemporary state of science, they conserve scien- 

 tific effort. Such a principle is of value regardless of its ultimate fate 

 and, quite plainly, it is no "mere convention." 



