THE PRINCIPLES OF SCIENCE 197 



not even appear in his statement of findings. Imagine, for example, 

 that I am a pre-Copernican astronomer puzzled by the striking fact 

 that when an exterior planet retrogrades it always stands in oppo- 

 sition to the sun. Finding this correlation inexplicable within the 

 framework of the Ptolemaic system, I set myself to discover its ori- 

 gin, and perhaps ultimately I hit upon the Copernican theory. I then 

 see how the odd correlation of retrograde and opposition may be 

 caused and, in my exposition of the Copernican system, I may well 

 cite this convincing explanation as an argument for acceptance of 

 that theory. But, quite emphatically, I will not state that the Co- 

 pernican system is the cause of this notable correlation. In some- 

 what the same fashion, first tidings of the existence of the Andes 

 mountains may at last explain for me a previously known occurrence 

 of a large high-altitude city like Quito, but I am unlikely to say that 

 the Andes cause Quito's high altitude. The scientist's search for 

 causes is but means to the end of understanding and, that under- 

 standing once achieved, his grasp of an entire system of phenomena 

 and explanations can no longer be expressed in necessarily fragmen- 

 tary statements about particular causes of particular phenomena. 



This curious disappearance of "cause" from the ultimate statements 

 of knowledge achieved through pursuit of causes encourages misin- 

 terpretation of the historical record— misinterpretation all the more 

 likely because several of the earlier scientists seem expressly to dis- 

 claim any interest in causes. Thus Galileo puts into the mouth of 

 Salviati the statement that: 



The present does not seem to be the proper time to investigate the 

 cause of the acceleration of natural motion, concerning which various 

 opinions have been expressed. ... At present it is the purpose of 

 our Author merely to investigate and to demonstrate some of the 

 properties of accelerated motion (whatever the cause of this accelera- 

 tion may be ) . . . 



In entirely similar fashion Boyle mentions the two models (plenist 

 and kinetic) that might explain the origin of the law that bears his 

 name, but he declines "to declare peremptorily for either of them 

 against the other" on the ground that: 



I shall decline meddling with a subject, which is much more hard to 

 be explicated than necessary to be so by him, whose business it is not, 

 in this letter, to assign the adequate cause of the spring of the air, but 



