“I don’t see that they had very much to do with his capture，” Ianswered.
“What you do in this world is a matter of no consequence，”
returned my companion， bitterly. “The question is， what canyou make people believe that you have done？ Never mind，” hecontinued， more brightly， after a pause. “I would not have missedthe investigation for anything. There has been no better casewithin my recollection. Simple as it was， there were several mostinstructive points about it.”
“Simple！” I ejaculated.
“Well， really， it can hardly be described as otherwise，” saidSherlock Holmes， smiling at my surprise. “The proof of itsintrinsic simplicity is， that without any help save a few veryordinary deductions I was able to lay my hand upon the criminalwithin three days.”
“That is true，” said I.
“I have already explained to you that what is out of the commonis usually a guide rather than a hindrance. In solving a problem ofthis sort， the grand thing is to be able to reason backwards. That isa very useful accomplishment， and a very easy one， but people donot practise it much. In the everyday affairs of life it is more usefulto reason forwards， and so the other comes to be neglected. Thereare fifty who can reason synthetically for one who can reasonanalytically.”
“I confess，” said I， “that I do not quite follow you.”
“I hardly expected that you would. Let me see if I can make itclearer. Most people， if you describe a train of events to them，will tell you what the result would be. They can put those eventstogether in their minds， and argue from them that somethingwill come to pass. There are few people， however， who， if youtold them a result， would be able to evolve from their own innerconsciousness what the steps were which led up to that result.
This power is what I mean when I talk of reasoning backwards， oranalytically.”
“I understand，” said I.
“Now this was a case in which you were given the result and hadto find everything else for yourself. Now let me endeavour to showyou the different steps in my reasoning. To begin at the beginning.
I approached the house， as you know， on foot， and with my mindentirely free from all impressions. I naturally began by examiningthe roadway， and there， as I have already explained to you， I sawclearly the marks of a cab， which， I ascertained by inquiry， musthave been there during the night. I satisfied myself that it was acab and not a private carriage by the narrow gauge of the wheels.
The ordinary London growler is considerably less wide than agentleman’s brougham.
“This was the first point gained. I then walked slowly downthe garden path， which happened to be composed of a clay soil，peculiarly suitable for taking impressions. No doubt it appearedto you to be a mere trampled line of slush， but to my trained eyesevery mark upon its surface had a meaning. There is no branch ofdetective science which is so important and so much neglected asthe art of tracing footsteps. Happily， I have always laid great stressupon it， and much practice has made it second nature to me. I sawthe heavy footmarks of the constables， but I saw also the trackof the two men who had first passed through the garden. It waseasy to tell that they had been before the others， because in placestheir marks had been entirely obliterated by the others comingupon the top of them. In this way my second link was formed，which told me that the nocturnal visitors were two in number， oneremarkable for his height （as I calculated from the length of hisstride） ， and the other fashionably dressed， to judge from the smalland elegant impression left by his boots.
“On entering the house this last inference was confirmed. Mywell-booted man lay before me. The tall one， then， had done themurder， if murder there was. There was no wound upon the deadman’s person， but the agitated expression upon his face assuredme that he had foreseen his fate before it came upon him. Menwho die from heart disease， or any sudden natural cause， never byany chance exhibit agitation upon their features. Having sniffedthe dead man’s lips， I detected a slightly sour smell， and I came tothe conclusion that he had had poison forced upon him. Again，I argued that it had been forced upon him from the hatred andfear expressed upon his face. By the method of exclusion， I hadarrived at this result， for no other hypothesis would meet thefacts. Do not imagine that it was a very unheard-of idea. Theforcible administration of poison is by no means a new thing incriminal annals. The cases of Dolsky in Odessa， and of Leturier inMontpellier， will occur at once to any toxicologist.