METHOD OF DISCOVERY 51 



something has opened the window. A second general 

 law that you have arrived at in the same way is, that 

 tea-pots and spoons do not go out of a window spontane- 

 ously, and you are satisfied that, as they are not now 

 where you left them, they have been removed. In the 

 third place, you look at the marks on the window-sill, and 

 the shoe-marks outside, and you say that in all previous 

 experience the former kind of mark has never been produced 

 by anything else but the hand of a human being ; and the 

 same experience shows that no other animal but man 

 at present wears shoes with hob-nails on them such as 

 would produce the marks in the gravel. I do not know, 

 even if we could discover any of those " missing links " 

 that are talked about, that they would help us to any 

 other conclusion I At any rate the law which states our 

 present experience is strong enough for my present purpose. 

 You next reach the conclusion, that as these kinds of 

 marks have not been left by any other animals than men, 

 or are liable to be formed in any other way than by a 

 man's hand and shoe, the marks in question have been 

 formed by a man in that way. You have, further, a 

 general law, founded on observation and experience, and 

 that, too, is, I am sorry to say, a very universal and unim- 

 peachable one, that some men are thieves ; and you 

 assume at once from all these premisses and that is what 

 constitutes your hypothesis that the man who made 

 the marks outside and on the window-sill, opened the 

 window, got into the room, and stole your tea-pot and 

 spoons. You have now arrived at a Vera Causa ; you 

 have assumed a Cause which it is plain is competent to 

 produce all the phenomena you have observed. You 

 can explain all these phenomena only by the hypothesis 

 of a thief. But that is a hypothetical conclusion, of 

 the justice of which you have no absolute proof at all ; 

 it is only rendered highly probable by a series of inductive 

 and deductive reasonings. 



I suppose your first action, assuming you are a man 

 of ordinary common sense, and that you have established 

 this hypothesis to your own satisfaction, will very likely 

 be to go off for the police, and set them on the track of 

 the burglar, with the view to the recovery of your property. 

 But just as you are starting with this object, some person 

 comes in, and on learning what you are about, says, " My 

 good friend, you are going on a great deal too fast. How 



