226 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 8 



with an unresolved dilemma, but if we take the idealistic view, the 

 principle becomes simply a statement of the object at which science 

 has aimed throughout its history. It is not my purpose to comment 

 on the age-old problem of idealism versus realism; I am concerned only 

 with the attitude implied in modern scientific developments. And the 

 point I want to emphasize as clearly and unmistakably as possible is 

 that anyone who regards the recent trend of physics in general, and the 

 theory of relativity in particular, as legitimate science or philosophy or 

 intellectual activity bearing whatever name may be thought honor- 

 able, must either be an idealist or presume that he is omniscient. I do 

 not wish in this place to plead the cause of either of the alternatives 

 open to the humble. I am not anxious to cry "Vote for realism, and 

 down with relativity!" or "Support idealism and relativity, and throw 

 realism to the dogs!" That is a matter for personal predilection, but it 

 is a matter for pure reason to show that those are the only alternatives 

 open to anyone who is not prepared to assume that he is omniscient. 



The striking divergence of opinion with which we opened can now, 

 I think, be understood. Those who, like M. Maritain and Mr. Eagle, 

 see the principle in question as an example of presumption arising from 

 ignorance, are realists — by which I mean that they instinctively think 

 as realists, whether or not they would accept the title. On the other 

 hand, those physicists and philosophers who accept the principle are, 

 by the same criterion, idealists, though most of them speak our ordi- 

 nary, everyday language which has accommodated itself to the realis- 

 tic outlook. In terms of that language their utterances necessarily 

 appear arrogant; what they apprehend instinctively as the wisdom of 

 a self-imposed discipline is clothed in sentences which suggest to the 

 realist the idea of arbitrary dogma. The divergence, arising as a 

 difference of philosophical attitude, is accentuated by the necessity of 

 expressing idealistic principles in realistic terms. 



Let me, in conclusion, recapitulate the argument. The practice of 

 modern physics is found on examination to imply that nothing must be 

 included in our description of the universe that would not be observable 

 if we had full control of all known means of observation. If we adopt 

 the realistic view that the universe exists independently of our obser- 

 vation of it, this implies that the means of observation which we al- 

 ready know are sufficient to reveal everything that exists. We must 

 in that case either make this assumption, for which we have no war- 

 rant, or else reject the recent developments of physics. If we choose 

 the second alternative, we are left without any assurance that we can 

 know anything of importance about what exists outside us. On the 

 other hand, if we adopt the idealistic view that the universe is con- 

 structed mentally by logical inference from experience, we see the im- 

 plication of modern physics as simply the traditional thesis of science 

 that the data we choose shall be pure experience, unalloyed with fancy 

 or arbitrary dogma. 



