THE EVOLUTION OF SCIENTIFIC THEORIES 287 



When an older theory is found insufficient, practically all its holding 

 of colligative relations will survive intact, rewoven in the pattern of 

 the new theory. When the older theory is a comparatively primitive 

 one, we readily understand how the few relations it accommodates 

 might be rewoven in short order. But when we come to deal with the 

 displacement of major theories, accommodating myriad relations, the 

 reweaving of all the separate relations in a drastically different pat- 

 tern appears no light undertaking. Indeed, were the relations wholly 

 separated, and the pattern wholly different, this might well prove an 

 almost impossible undertaking. 



From the fact that the reweaving of even major theoretic patterns 

 is completed reasonably promptly, we infer the presence of some 

 further element of continuity in the sequence of scientific theories. 

 To be sure, sometimes the older theory is not so much destroyed as 

 —rather in the manner of the duck by Peter's wo\i— engulfed entire 

 by the new. Thus classical electrodynamics was esteemed beautiful 

 at least in part because of the extraordinarily high value of its cor- 

 relative index. In quantum mechanics we acquire a system of still 

 higher correlative index which, Dirac suggests, incorporates the clas- 

 sical system virtually en bloc. 



This is brought about by the fact that the changes made in the 

 classical theory are very few in number, although they are of a funda- 

 mental nature and involve the introduction of entirely new concepts, 

 and are such that practically all the features of the classical theory to 

 which it owes its attractiveness can be taken over unchanged into 

 the new theory. 



The correspondence principle. Perhaps the most striking element 

 of continuity in organic evolution is the survival in newer species of 

 major parts of the structural organization found in the old. In the 

 succession of recent scientific theories we find a similar profoundly 

 evolutionary development. Sambursky emphasizes the generality of 

 the relation of correspondence he considers to obtain between rela- 

 tivistic and classical mechanics : 



In spite of the theoretical and philosophical difference between classi- 

 cal mechanics and the new [relativistic] theory, and in spite of the 

 formal difference in their mathematical method, the former is still in- 

 cluded in the latter as a first approximation. History of science in the 



