546 THE POPULAR SCIENCE MONTHLY. 



classical quotation. They " cudgel their brains," to use a common ex 

 pression, and are unsuccessful; they give their minds to something en- 

 tirely different ; and some hours afterward, when their thoughts are 

 far away from the subject on which they had been concentrating them 

 with the idea of recovering this lost clew, the thing flashes into the 

 mind. Now, this is so common an occurrence, that we pass it by with- 

 out taking particular note of it ; and yet I believe that the inquiry into 

 the real nature of this occurrence may lead us to understand something 

 of the inner mechanism of our own minds which we shall find to be 

 very useful to us. 



There is another point, however, arising out of the story which I 

 have just told you, upon which again I would fix your attention : Why 

 and how did the detective arrive at this assurance from the result of 

 his inquiries? It was a matter of judgment based upon long practice 

 and experience, which had given him that kind of insight into the 

 characters, dispositions, and nature of the persons who were brought 

 before him, which only those who have got this faculty as an original 

 gift, or have acquired it by very long experience, can possess with 

 any thing like that degree of assurance which he was able to entertain. 

 I believe that this particular power of the detective is, so to speak, an 

 exaltation in a particular direction of what we call " common-sense." 

 We are continually bringing to the test of this common-sense a great 

 number of matters which we cannot decide by reason ; a number of 

 matters as to which, if we were to begin to argue, there may be so 

 much to be said on both sides, that we may be unable to come to a 

 conclusion. And yet, with regard to a great many of these subjects 

 some of which I shall have to discuss in my next lecture we consider 

 that common-sense gives us a much better result than any elaborate 

 discussion. Now, I will give you an illustration of this which you will 

 all readily comprehend : Why do we believe in an external world ? 

 Why do I believe that I have at present before me many hundreds of 

 intelligent auditors, looking up and listening to every word that I 

 say ? Why do you believe that you are hearing me lecture ? You 

 will say at once that your common-sense tells you. I see you ; you 

 see and hear me ; and I know that I am addressing you. But if once 

 this subject is logically discussed, if once we go into it on the basis of 

 a pure reasoning process, it is found really impossible to construct such 

 a proof as shall satisfy every logician. As far as my knowledge ex- 

 tends, every logician is able to pick a hole in every other logician's 

 proof. Now, here we have, then, a case obvious to you all, in which 

 common-sense decides for us without any doubt or hesitation at all. 

 And I venture to use an expression upon this point which has been 

 quoted with approval by one of the best logicians and metaphysicians 

 of our time, Archbishop Manning, who cited the words that I have 

 used, and entirely concurred in them, namely, that " in regard to the 

 existence of the external world the common-sense decision of mankind 



