100 MR. DARWIN'S WORK AND 



how the planets revolve, and how they are maintained in 

 their orbits, you cannot tell us wfcat is the cause of the 

 origin of the sun, moon, and stars. So what is the use 

 of what you have done ? " Yet these objections would not 

 be one whit more preposterous than the objections which 

 have been made to the Origin of Species. Mr. Darwin, 

 then, had a perfect right to limit his inquiry as he pleased, 

 and the only question for us the inquiry being so limited 

 is 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 pheno- 

 mena with a view to get at its cause, is always the same ; 

 in all cases we must invent an hypothesis ; we must place 

 before ourselves some more or less likely supposition 

 respecting that cause ; and then, having assumed an 

 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 (lie logicians call vrrci am.s.r true causes ; 

 in the next place, we should be prepared to show that the 

 assumed causes of the phenomena are competent to produce 

 such phenomena as those which we wish to explain by 

 them ; and in the last place, \ve ought to be able to show 

 that no other known causes are competent to produce 

 these phenomena. It we can succeed in satisfying these 

 three conditions we shall have demonstrated our hypo- 

 thesis ; or rather I ought to say, we shall have proved 

 it as far as certainty is possible for us ; for, after all, there 



