SCIENTIFIC INVESTIGATION 91 



is, I am sorry to say, a very universal and unimpeacha- 

 ble 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 hy- 

 pothesis of a thief. But that is a hypothetical conclu- 

 sion, 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 that you are a 

 man of ordinary common sense, and that you have es- 

 tablished 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 do you know that the man 

 who really made the marks took the spoons ? It might 

 have been a monkey that took them, and the man may 

 have merely looked in afterwards." You would prob- 

 ably reply, "Well, that is all very well, but you see it 

 is contrary to all experience of the way tea-pots and 

 spoons are abstracted ; so that, at any rate, your hypo- 

 thesis is less probable than mine." While you are talk- 

 ing the thing over in this way, another friend arrives, 

 one of the good kind of people that I was talking of a 

 little while ago. And he might say, " Oh, my dear sir, 

 you are certainly going on a great deal too fast. You 



