Theories and Guesses 285 



They were elaborated into the doctrine of uniformitarian- 

 ism, and in the minds of scientists they shattered the cata- 

 clysms of Cuvier. With all due allowances for errors in 

 details of observation and inference, the doctrine of uni- 

 formitarianism remains after all the only sound principle 

 for any attempt at understanding the world scientifically. 

 It means, in effect, that in our efforts to interpret the facts 

 of nature we must rely upon what we know positively. 

 Where known agencies and forces can be made to serve, we 

 must avoid improvising agencies and forces to explain 

 events. It is of course impossible to '* know " that processes 

 which are going on before our eyes were going on before 

 our days, or will continue to go on after we stop watching. 

 It seems, nevertheless, much more reasonable to assume con- 

 tinuity of essential characteristics of the materials and forces 

 of the world than to resort to the interposition of mysterious 

 agencies of whose nature we know nothing. 



Theories and Guesses 



Although it is true that we can never have any direct 

 knowledge about the historical past, it does not follow that 

 one surmise is as good as another. We have unfortunately 

 suffered incalculably in the course of our cultural growth 

 from the vulgar assumption that in the absence of direct 

 knowledge we have either to accept the teachings of inspired 

 authority or remain free to make up our own guesses. The 

 scientist formulates theories and hypotheses which, from the 

 nature of the case, cannot be immediately or directly demon- 

 strated as " true." But these theories are not free or irre- 

 sponsible guesses. They are reasoned constructions that are 

 controlled by previous experience and knowledge, and 

 that are subjected to further control through logical 

 criticism and careful checking against the facts of observa- 

 tion and experiment. It is as futile and puerile as it is 

 unfair to identify such mental products with guesses and 

 opinions. 



