374 THE REAL WORLD 



comparisons with experiment is actually positively advantageous. 

 For example, it often allows us to resolve situations of deadlock exist- 

 ing within the domain of one particular science. Thus for some years 

 no astronomical observation was competent to resolve the deadlock 

 of Copernican and Tychonic astronomies. But the deadlock in as- 

 tronomy is broken by the Newtonian reconstruction of physics. To- 

 gether Copernican astronomy and Newtonian physics form a coher- 

 ent theoretic system of immense correlative index; and nothing of 

 the sort is found possible when Tychonic astronomy is "held true." 

 Such considerations determine also the acceptability of our most 

 fundamental substantive and regulative principles. 



PRINCIPLES 



In the short term, scientific work is dominated by principles we are 

 resolved to maintain come what may. Were they invariably held true 

 then indeed science might tell us far less of the nature of the world 

 than of ourselves, who choose and enforce these principles. Theories 

 shaped to conform with such principles guide our observations and 

 experiments, and the interpretation of the results so obtained is di- 

 rected by the selfsame principles. Can we then at all hope to recog- 

 nize a failure of some such principle? Of course we can: demonstra- 

 bly our principles have changed! Meyerson comments: 



It is we who try to establish identity in nature, . . . And that is 

 what we call understanding and explaining nature. It yields itself to 

 a certain extent, but it also resists. Reality rebels and does not allow us 

 to denv it. 



Meeting resistance and rebellion, and bringing ourselves to recognize 

 it as such, we do "let natvire train us" even as regards articles of scien- 

 tific faith as fundamental as those noted by Weizsacker. 



Thus we apply successively to our measuring instruments Euclidean 

 geometry, the law of causality, and the category of substances; but it 

 is with these very instruments that we discover phenomena for which 

 those same principles are no longer adequate. 



How does such inadequacy manifest itself? In the 18th century 

 Kant felt that Euclidean geometry could never be challenged, be- 1 

 cause we cannot view the world save in Euclidean terms. Even at the ' 

 beginning of the 20th century Poincare felt that Euclidean geometry 



