24 FROM THE GREEKS TO DARWIN 



important feature in the intellectual environ- 

 ment of the evolution idea. Now working, as a 

 matter of course, by the observe-and-guess or the 

 induction-deductive method — first observing a 

 few facts, for a preliminary induction or 'work- 

 ing hypothesis' which we apply tentatively to ex- 

 plain certain classes of facts — we hardly appre- 

 ciate that this effective mental machinery is a 

 comparatively recent discovery. The fate of a 

 'working hypothesis' depends upon its applica- 

 tion to every single fact. When, therefore, some 

 obstinate or newly discovered fact compels us to 

 abandon one 'working hypothesis' which for a 

 time has not only satisfied but served us, and to 

 construct another, and when finally, after see- 

 sawing between observation and speculation, we 

 experience the pleasure of extracting the truth, 

 we have meanwhile run up an unpayable debt to 

 the past. 



The early Greeks were mainly deductive or a 

 priori in their method. Aristotle, coming at a 

 much later period, after natural methods of in- 

 terpretation had been studied, understood and 

 taught the method of scientific induction almost 

 as clearly as Bacon, but he mainly practised de- 

 duction. This was well, for in Aristotle's period 

 and during his lifetime, few steps in advance 

 could have been made by the safer method of in- 

 duction, while he unquestionably promoted many 



