130 mr. darwin's work and 



to ascertain whether the method of his inquiry is sound 

 or unsound ; whether he has obeyed the canons which 

 must guide and govern all investigation, or whether he 

 has broken them ; and it was because our inquiry this 

 evening is essentially limited to that question that I 

 spent a good deal of time in a former lecture (which, 

 perhaps some of you thought might have been better 

 employed) in endeavouring to illustrate the method and 

 nature of scientific inquiry in general. We shall now 

 have to put in practice the principles that I then laid 

 down. 



I stated to you in substance, if not in words, that 

 wherever there are complex masses of phenomena to be 

 inquired into, whether they be phenomena of the affairs 

 of daily life, or whether they belong to the more abstruse 

 and difficult problems laid before the philosopher, our 

 course of proceeding in unravelling that complex chain 

 of phenomena with a view to get at its cause, is always 

 the same ; in all cases we must invent a hypothesis ; we 

 must place before ourselves some more or less likely 

 supposition respecting that cause ; and then, having 

 assumed a hypothesis, having supposed a cause for the 

 phenomena in question, we must endeavour, on the one 

 hand, to demonstrate our hypothesis, or, on the other, to 

 upset and reject it altogether, by testing it in three 

 ways. We must, in the first place, be prepared to 

 prove that the supposed causes of the phenomena 

 exist in nature ; that they are what the logicians 

 call vera causae — true causes ; — in the next place, we 

 should be prepared to show that the assumed causes of 

 the phenomena are competent to produce such pheno- 

 mena as those which we wish to explain by them ; and 

 in the last place, we ought to be able to show that no 



