Sherlock Holmes & Deduction: A Writer's Guide

Holmes’ approach to the Science of Deduction – tips, clues and details to writing the deductive reasoning of Sherlock Holmes – A resource for Mystery Authors

While writing the Supernatural Case-Files of Sherlock Holmes, one of the most difficult facets was attempting to duplicate Holmes’ amazing powers of deduction with the same flavor and flare that Doyle did. 
How much can Holmes know from a murder scene?  How do we write a mystery with a character like Holmes in it, and still preserve any element of suspense for the reader?  What does Holmes know partway through any given story compared to what Watson knows, and is the reader somewhere between these two points, or somewhere entirely differently.
It’s a daunting task.
Grappling with these details, in addition to the expected and not-insignificant task of evoking Holmes, Watson, London and Doyle’s flare for the dramatic called for an enormous amount of research.  I usually spend as much time planning and outlining one of these stories (usually about twice the length of most of the original stories) as I do planning out my original full-length novels.
Not surprisingly, the best source for research was Doyle himself.  So what follows is the fruits of that research, namely, the details of every deduction: snipped out and categorized into sections (People, Letters, Ashes, Tracks, etc.) for easy reference, with the original references so you can find what story it came from.  I did this in story order, so the many deductions from ‘A Study in Scarlet’ head most of these lists. 
Also, this list is not complete.  I usually work on it every time I start a new Holmes story, and get yanked away as the task accomplishes its goal of giving the data I need.  Currently, I’ve culled all the way through to The Adventure of the Norwood Builder in The Return of Sherlock Holmes.  This is page 423 out of 987 in my version of the Canon, so only about halfway through.  Still, since it’s served its purpose for a number of times, I thought it might be useful to other pastichers wanting to inflict their narratives on the long-suffering public.  


Watson was lately from Afghanistan: 'Here is a gentleman of a medical type, but with the air of a military man. Clearly an army doctor, then. He has just come from the tropics, for his face is dark, and that is not the natural tint of his skin, for his wrists are fair. He has undergone hardship and sickness, as his haggard face says clearly. His left arm has been injured. He holds it in a stiff and unnatural manner. Where in the tropics could an English army doctor have seen much hardship and got his arm wounded? Clearly in Afghanistan.'

Watson's Trip to the Post-Office:
"Observation tells me that you have a little reddish mould adhering to your instep. Just opposite the Seymour Street Office they have taken up the pavement and thrown up some earth which lies in such a way that it is difficult to avoid treading in it in entering. The earth is of this peculiar reddish tint which is found, as far as I know, nowhere else in the neighborhood." [How, then, did you deduce the telegram?] "Why, of course I knew that you had not written a letter, since I sat opposite to you all morning. I see also in your open desk there that you have a sheet of stamps and a thick bundle of post-cards. What could you go into the post-office for, then, but to send a wire? Eliminate all other factors, and the one which remains must be the truth."

Watson had recently started Doctor Profession:
"Wedlock suits you," he remarked. "I think, Watson, that you have put on seven and a half pounds since I saw practice again, I observe...I see it, I deduce it. How do I know that you have been getting yourself very wet lately, and that you have a most clumsy and careless servant girl? eyes tell me that on the inside of your left shoe, just where the firelight strikes it, the leather is scored by six almost parallel cuts. Obviously they have been caused by someone who has very carelessly scraped round the edges of the sole in order to remove crusted mud from it...Hence, you see, my double deduction that you had been out in vile weather, and that you had a particularly malignant boot-slitting specimen of the London slavey. As to your practice, if a gentleman walks into my rooms smelling of iodoform, with a black mark of nitrate of silver upon his right forefinger, and a bulge on the right side of his top-hat to show where he has secreted his stethoscope, I must be dull, indeed, if I do not pronounce him to be an active member of the medical profession.”

Watson's Shaving:
"I very clearly perceive that in your bedroom the window is upon the right-hand side...I know the military neatness which characterizes you. You shave every morning, and in this season you shave by the sunlight; but since your shaving is less and less complete as we get farther back on the left side, until it becomes positively slovenly as we get round the angle of the jaw, it is surely very clear that that side is less illuminated than the other. I could not imagine a man of your habits looking at himself in an equal light and being satisfied with such a result.

Watson's Cold:
"I perceive that you have been unwell lately. Summer colds are always a little trying.”
"I was confined to the house by a sever chill for three days last week. I thought, however, that I had cast off every trace of it.”
"So you have. You look remarkably robust"..."Your slippers are new," he said. "You could not have had them more than a few weeks. The soles which you are at this moment presenting to me are slightly scorched. For a moment I thought they might have got wet and been burned in the drying. But near the instep there is a small circular wafer of paper with the shopman's hieroglyphics upon it. Damp would of course have removed this. You had, then, been sitting with our feet outstretched to the fire, which a man would hardly do even in so wet a June as this if he were in his full health.”

Watson in the Crooked Man:
You still smoke the Arcadia mixture of your bachelor days then! There's no mistaking that fluffy ash upon your coat. It's easy to tell that you have been accustomed to wear a uniform, Watson. You'll never pass as a pure-bred civilian as long as you keep that habit of carrying your handkerchief in your sleeve.
I see that you are professionally rather busy just now…I have the advantage of knowing your habits…When your round is a short one you walk, and when it is a long one you use a hansom. As I perceive that your boots, although used, are by no means dirty, I cannot doubt that you are at present busy enough to justify the hansom.”

Identifying Retired Sergeant of Marines: Even across the street I could see a great blue anchor tattooed on the back of the fellow's hand. That smacked of the sea. He had a military carriage, however, and regulation side whiskers. There we have the marine. He was a man with some amount of self-importance and a certain air of command. You must have observed the way in which he held his head and swung his cane. A steady, respectable, middle-aged man, too, on the face of him—all facts which led me to believe that he had been a sergeant."

Examining the Corpse of Bartholemew Sholto:
"The muscles are as hard as a board," I answered.
"Quite so. They are in a state of extreme contraction, far exceeding the usual rigor mortis. Coupled with this distortion of the face, this Hippocratic smile, or 'risus sardonicus,' as the old writers called it, what conclusion would it suggest to your mind?"
"Death from some powerful vegetable alkaloid," I answered,—"some strychnine-like substance which would produce tetanus."

Jabez Wilson in the Red-Headed League:
"Beyond the obvious facts that he has at some time done manual labour, that he takes snuff, that he is a Freemason, that he has been in China, and that he has done a considerable amount of writing lately, I can deduce nothing else...Your right hand is quite a size larger than your left. You have worked with it, and the muscles are more developed...rather against the strict rules of your order, you use an arc-and-compass breastpin...What else can be indicated by that right cuff so very shiny for five inches, and the left one with the smooth patch near the elbow where you rest it upon the desk?...The fish that you have tattooed immediately above your right wrist could only have been done in China. I have made a small study of tattoo marks and have even contributed to the literature of the subject. That trick of staining the fishes' scales of a delicate pink is quite peculiar to China. When, in addition, I see a Chinese coin hanging from your watch-chain, the matter becomes even more simple.”

Mary Sutherland in Case of Identity
As you observe, this woman had plush upon her sleeves, which is a most useful material for showing traces. The double line a little above the wrist, where the typewritist presses against the table, was beautifully defined. The sewing-machine, of the hand type, leaves a similar mark, but only on the left arm, and on the side of it farthest from the thumb, instead of being right across the broadest part, as this was. I then glanced at her face, and, observing the dint of a pince-nez at either side of her nose, I ventured a remark upon short sight and typewriting, which seemed to surprise her...I was then much surprised and interested on glancing down to observe that, though the boots which she was wearing were not unlike each other, they were really odd ones; the one having a slightly decorated toe-cap, and the other a plain one. One was buttoned only in the two lower buttons out of five, and the other at the first, third, and fifth. Now, when you see that a young lady, otherwise neatly dressed, has come away from home with odd boots, half-buttoned, it is no great deduction to say that she came away in a hurry....I noted, in passing, that she had written a note before leaving home but after being fully dressed. You observed that her right glove was torn at the forefinger, but you did not apparently see that both glove and finger were stained with violet ink. She had written in a hurry and dipped her pen too deep. It must have been this morning, or the mark would not remain clear upon the finger."

John Openshaw in the Five Orange Pips:
You have come up from the south-west, I see,”
"Yes, from Horsham.”
"That clay and chalk mixture which I see upon your toe caps is quite distinctive.”

Helen Stoner in the Speckled Band:
"You must not fear," said he soothingly, bending forward and patting her forearm. "We shall soon set matters right, I have no doubt. You have come in by train this morning, I see.”
"You know me, then?”
"No, but I observe the second half of a return ticket in the palm of your left glove. You must have started early, and yet you had a good drive in a dog-cart, along heavy roads, before you reached the station.”
The lady gave a violent start and stared in bewilderment at my companion.
"There is no mystery, my dear madam," said he, smiling. "The left arm of your jacket is spattered with mud in no less than seven places. The marks are perfectly fresh. There is no vehicle save a dog-cart which throws up mud in that way, and then only when you sit on the left-hand side of the driver.”

Mr. Trevor in Gloria Scott
'I might suggest that you have gone about in fear of some personal attack with the last twelvemonth.'..."'You have a very handsome stick,' I answered. 'By the inscription I observed that you had not had it more than a year. But you have taken some pains to bore the head of it and pour melted lead into the hole so as to make it a formidable weapon. I argued that you would not take such precautions unless you had some danger to fear.'..."'You have boxed a good deal in your youth.'...your ears. They have the peculiar flattening and thickening which marks the boxing man.'..."'You have done a good deal of digging by your callosities.'..."'And you have been most intimately associated with some one whose initials were J. A., and whom you afterwards were eager to entirely forget.'...'When you bared your arm to draw that fish into the boat I saw that J. A. Had been tattooed in the bend of the elbow. The letters were still legible, but it was perfectly clear from their blurred appearance, and from the staining of the skin round them, that efforts had been made to obliterate them. It was obvious, then, that those initials had once been very familiar to you, and that you had afterwards wished to forget them.'

The Dead man in Reigate Puzzle:
The wound upon the dead man was, as I was able to determine with absolute confidence, fired from a revolver at the distance of something over four yards. There was no powder-blackening on the clothes.

Mycroft and Sherlock’s duel of deductions on a passerby in the street in The Greek Interpreter
"The billiard-marker and the other?” [spoken by Sherlock]
"Precisely. What do you make of the other?”
The two men had stopped opposite the window. Some chalk marks over the waistcoat pocket were the only signs of billiards which I could see in one of them. The other was a very small, dark fellow, with his hat pushed back and several packages under his arm.
"An old soldier, I perceive," said Sherlock.
"And very recently discharged," remarked the brother.
"Served in India, I see.”
"And a non-commissioned officer.”
"Royal Artillery, I fancy," said Sherlock.
"And a widower.”
"But with a child.”
"Children, my dear boy, children.”
"Come," said I, laughing, "this is a little too much.”
"Surely," answered Holmes, "it is not hard to say that a man with that bearing, expression of authority, and sunbaked skin, is a soldier, is more than a private, and is not long from India.”
"That he has not left the service long is shown by his still wearing is ammunition boots, as they are called," observed Mycroft.
"He had not the cavalry stride, yet he wore his hat on one side, as is shown by the lighter skin of that side of his brow. His weight is against his being a sapper. He is in the artillery.”
"Then, of course, his complete mourning shows that he has lost some one very dear. The fact that he is doing his own shopping looks as though it were his wife. He has been buying things for children, you perceive. There is a rattle, which shows that one of them is very young. The wife probably died in childbed. The fact that he has a picture-book under his arm shows that there is another child to be thought of.”

Joseph Harris in The Naval Treaty:
"I perceive that you are not yourself a member of the family.”
Our acquaintance looked surprised, and then, glancing down, he began to laugh.
"Of course you saw the J H monogram on my locket," said he. "For a moment I thought you had done something clever.”

Lord Holdhurst in The Naval Treaty:
"He's a fine fellow," said Holmes, as we came out into Whitehall. "But he has a struggle to keep up his position. He is far from rich and has many calls. You noticed, of course, that his boots had been resoled.


Looking over Watson's watch:
"...the watch belonged to your elder brother, who inherited it from your father."
"That you gather, no doubt, from the H. W. upon the back?"
"Quite so. The W. suggests your own name. The date of the watch is nearly fifty years back, and the initials are as old as the watch: so it was made for the last generation. Jewelry usually descends to the eldest son, and he is most likely to have the same name as the father. Your father has, if I remember right, been dead many years. It has, therefore, been in the hands of your eldest brother."
"Right, so far," said I. "Anything else?"
"He was a man of untidy habits,—very untidy and careless. He was left with good prospects, but he threw away his chances, lived for some time in poverty with occasional short intervals of prosperity, and finally, taking to drink, he died. That is all I can gather."
I sprang from my chair and limped impatiently about the room with considerable bitterness in my heart.
"This is unworthy of you, Holmes," I said. "I could not have believed that you would have descended to this. You have made inquires into the history of my unhappy brother, and you now pretend to deduce this knowledge in some fanciful way. You cannot expect me to believe that you have read all this from his old watch! It is unkind, and, to speak plainly, has a touch of charlatanism in it."
"My dear doctor," said he, kindly, "pray accept my apologies. Viewing the matter as an abstract problem, I had forgotten how personal and painful a thing it might be to you. I assure you, however, that I never even knew that you had a brother until you handed me the watch."
"Then how in the name of all that is wonderful did you get these facts? They are absolutely correct in every particular."
"Ah, that is good luck. I could only say what was the balance of probability. I did not at all expect to be so accurate."
"But it was not mere guess-work?"
"No, no: I never guess. It is a shocking habit,—destructive to the logical faculty. What seems strange to you is only so because you do not follow my train of thought or observe the small facts upon which large inferences may depend. For example, I began by stating that your brother was careless. When you observe the lower part of that watch-case you notice that it is not only dinted in two places, but it is cut and marked all over from the habit of keeping other hard objects, such as coins or keys, in the same pocket. Surely it is no great feat to assume that a man who treats a fifty-guinea watch so cavalierly must be a careless man. Neither is it a very far-fetched inference that a man who inherits one article of such value is pretty well provided for in other respects."
I nodded, to show that I followed his reasoning.
"It is very customary for pawnbrokers in England, when they take a watch, to scratch the number of the ticket with a pin-point upon the inside of the case. It is more handy than a label, as there is no risk of the number being lost or transposed. There are no less than four such numbers visible to my lens on the inside of this case. Inference,—that your brother was often at low water. Secondary inference,—that he had occasional bursts of prosperity, or he could not have redeemed the pledge. Finally, I ask you to look at the inner plate, which contains the key-hole. Look at the thousands of scratches all round the hole,—marks where the key has slipped. What sober man's key could have scored those grooves? But you will never see a drunkard's watch without them. He winds it at night, and he leaves these traces of his unsteady hand. Where is the mystery in all this?"

The Top Hat in Blue Carbuncle:
That the man was highly intellectual is of course obvious upon the face of it, and also that he was fairly well-to-do within the last three years, although he has now fallen upon evil days. He had foresight, but has less now than formerly, pointing to a moral retrogression, which, when taken with the decline of his fortunes, seems to indicate some evil influence, probably drink, at work upon him. This may account also for the obvious fact that his wife has ceased to love him.”
"My dear Holmes!”
"He has, however, retained some degree of self-respect," he continued, disregarding my remonstrance. "He is a man who leads a sedentary life, goes out little, is out of training entirely, is middle-aged, has grizzled hair which he has had cut within the last few days, and which he anoints with lime-cream. These are the more patent facts which are to be deduced from his hat. Also, by the way, that it is extremely improbable that he has gas laid on in his house.”
"You are certainly joking, Holmes.”
"Not in the least. Is it possible that even now, when I give you these results, you are unable to see how they are attained?”
"I have no doubt that I am very stupid, but I must confess that I am unable to follow you. For example, how did you deduce that this man was intellectual?”
For answer Holmes clapped the hat upon his head. It came right over the forehead and settled upon the bridge of his nose. "It is a question of cubic capacity," said he; "a man with so large a brain must have something in it.”
"The decline of his fortunes, then?”
"This hat is three years old. These flat brims curled at the edge came in then. It is a hat of the very best quality. Look at the band of ribbed silk and the excellent lining. If this man could afford to buy so expensive a hat three years ago, and has had no hat since, then he has assuredly gone down in the world.”
"Well, that is clear enough, certainly. But how about the foresight and the moral retrogression?”
Sherlock Holmes laughed. "Here is the foresight," said he putting his finger upon the little disc and loop of the hat-securer.
"They are never sold upon hats. If this man ordered one, it is a sign of a certain amount of foresight, since he went out of his way to take this precaution against the wind. But since we see that he has broken the elastic and has not troubled to replace it, it is obvious that he has less foresight now than formerly, which is a distinct proof of a weakening nature. On the other hand, he has endeavored to conceal some of these stains upon the felt by daubing them with ink, which is a sign that he has not entirely lost his self-respect.”
"Your reasoning is certainly plausible.”
"The further points, that he is middle-aged, that his hair is grizzled, that it has been recently cut, and that he uses limecream, are all to be gathered from a close examination of the lower part of the lining. The lens discloses a large number of hair-ends, clean cut by the scissors of the barber. They all appear to be adhesive, and there is a distinct odour of lime-cream. This dust, you will observe, is not the gritty, gray dust of the street but the fluffy brown dust of the house, showing that it has been hung up indoors most of the time, while the marks of moisture upon the inside are proof positive that the wearer perspired very freely, and could therefore, hardly be in the best of training.”
"But his wife--you said that she had ceased to love him.”
"This hat has not been brushed for weeks. When I see you, my dear Watson, with a week's accumulation of dust upon your hat, and when your wife allows you to go out in such a state, I shall fear that you also have been unfortunate enough to lose your wife's affection.”
"But he might be a bachelor.”
"Nay, he was bringing home the goose as a peace-offering to his wife. Remember the card upon the bird's leg.”
"You have an answer to everything. But how on earth do you deduce that the gas is not laid on in his house?”
"One tallow stain, or even two, might come by chance; but when I see no less than five, I think that there can be little doubt that the individual must be brought into frequent contact with burning tallow--walks upstairs at night probably with his hat in one hand and a guttering candle in the other. Anyhow, he never got tallow-stains from a gas-jet.

Grant Munroe's Pipe in Yellow Stain:
"Pipes are occasionally of extraordinary interest," said he. "Nothing has more individuality, save perhaps watches and bootlaces. The indications here, however, are neither very marked nor very important. The owner is obviously a muscular man, left-handed, with an excellent set of teeth, careless in his habits, and with no need to practise economy.”
My friend threw out the information in a very offhand way, but I saw that he cocked his eye at me to see if I had followed his reasoning.
"You think a man must be well-to-do if he smokes a seven-shilling pipe," said I.
"This is Grosvenor mixture at eightpence an ounce," Holmes answered, knocking a little out on his palm. "As he might get an excellent smoke for half the price, he has no need to practise economy.”
"And the other points?”
"He has been in the habit of lighting his pipe at lamps and gas-jets. You can see that it is quite charred all down one side. Of course a match could not have done that. Why should a man hold a match to the side of his pipe? But you cannot light it at a lamp without getting the bowl charred. And it is all on the right side of the pipe. From that I gather that he is a left-handed man. You hold your own pipe to the lamp, and see how naturally you, being right-handed, hold the left side to the flame. You might do it once the other way, but not as a constancy. This has always been held so. Then he has bitten through his amber. It takes a muscular, energetic fellow, and one with a good set of teeth, to do that.

The Forced Door in the Reigate Puzzle:
Holmes made an examination of the door which had been forced. It was evident that a chisel or strong knife had been thrust in, and the lock forced back with it. We could see the marks in the wood where it had been pushed in.
The Hatstand in Crooked Man:
I see that you have no gentleman visitor at present. Your hat-stand proclaims as much.

The Floor and step of Watson’s House in Crooked Man:
Sorry to see that you've had the British workman in the house. He's a token of evil. …He has left two nail-marks from his boot upon your linoleum just where the light strikes it.

The basket of objects inside Dr. Trevelyan’s brougham (carriage) in The Resident Patient:
"Hum! A doctor's--general practitioner, I perceive," said Holmes. "Not been long in practice, but has had a good deal to do. Come to consult us, I fancy! Lucky we came back!”
I was sufficiently conversant with Holmes's methods to be able to follow his reasoning, and to see that the nature and state of the various medical instruments in the wicker basket which hung in the lamplight inside the brougham had given him the data for his swift deduction.

The candle in Resident Patient:
"Good-evening, doctor," said Holmes, cheerily. "I am glad to see that you have only been waiting a very few minutes….it was the candle on the side-table that told me.”

Blessington’s Room in the Resident Patient:
[from Detective Lanner]
The bed has been well slept in, you see. There's his impression deep enough. It's about five in the morning, you know, that suicides are most common. That would be about his time for hanging himself. It seems to have been a very deliberate affair.”
"I should say that he has been dead about three hours, judging by the rigidity of the muscles," said I.  [Watson]

Papers, Notes & Letters:

Letter in Scandal in Bohemia: I carefully examined the writing, and the paper upon which it was written.
"The man who wrote it was presumably well to do," I remarked, endeavoring to imitate my companion's processes. "Such paper could not be bought under half a crown a packet. It is peculiarly strong and stiff.”
"Peculiar--that is the very word," said Holmes. "It is not an English paper at all. Hold it up to the light.”
I did so, and saw a large "E" with a small "g," a "P," and a large "G" with a small "t" woven into the texture of the paper.
"What do you make of that?" asked Holmes.
"The name of the maker, no doubt; or his monogram, rather.”
"Not at all. The 'G' with the small 't' stands for 'Gesellschaft,' which is the German for 'Company.' It is a customary contraction like our 'Co.' 'P,' of course, stands for 'Papier.' Now for the 'Eg.' Let us glance at our Continental Gazetteer." He took down a heavy brown volume from his shelves.
"Eglow, Eglonitz--here we are, Egria. It is in a German-speaking country--in Bohemia, not far from Carlsbad. 'Remarkable as being the scene of the death of Wallenstein, and for its numerous glass-factories and paper-mills.' Ha, ha, my boy, what do you make of that?" His eyes sparkled, and he sent up a great blue triumphant cloud from his cigarette.
"The paper was made in Bohemia," I said.
"Precisely. And the man who wrote the note is a German. Do you note the peculiar construction of the sentence--'This account of you we have from all quarters received.' A Frenchman or Russian could not have written that. It is the German who is so uncourteous to his verbs.

Envelope: "I perceive also that whoever addressed the envelope had to go and inquire as to the address.”
"How can you tell that?”
"The name, you see, is in perfectly black ink, which has dried itself. The rest is of the grayish color, which shows that blotting-paper has been used. If it had been written straight off, and then blotted, none would be of a deep black shade. This man has written the name, and there has then been a pause before he wrote the address, which can only mean that he was not familiar with it. It is, of course, a trifle, but there is nothing so important as trifles.

"...a typewriter has really quite as much individuality as a man's handwriting. Unless they are quite new, no two of them write exactly alike. Some letters get more worn than others, and some wear only on one this every case there is some little slurring over of the 'e,' and a slight defect in the tail of the 'r.' I have here four letters which purport to come from the missing man...not only are the 'e's' slurred and the 'r's' tailless, but you will observe, if you care to use my magnifying lens, that the fourteen other characteristics to which I have alluded are there as well.”

Mary Morstan's Note from Thaddeus Sholto:
"They are disguised hands, except the letter," he said, presently, "but there can be no question as to the authorship. See how the irrepressible Greek e will break out, and see the twirl of the final s. They are undoubtedly by the same person.
[On the writer's character]: "Look at his long letters," he said. "They hardly rise above the common herd. That d might be an a, and that l an e. Men of character always differentiate their long letters, however illegibly they may write. There is vacillation in his k's and self-esteem in his capitals."

Map in Sign of the Four:
"It is paper of native Indian manufacture," he remarked. "It has at some time been pinned to a board. The diagram upon it appears to be a plan of part of a large building with numerous halls, corridors, and passages. At one point is a small cross done in red ink, and above it is '3.37 from left,' in faded pencil-writing. In the left-hand corner is a curious hieroglyphic like four crosses in a line with their arms touching. Beside it is written, in very rough and coarse characters, 'The sign of the four,—Jonathan Small, Mahomet Singh, Abdullah Khan, Dost Akbar.' No, I confess that I do not see how this bears upon the matter. Yet it is evidently a document of importance. It has been kept carefully in a pocket-book; for the one side is as clean as the other."

Torn Letter in Reigate Puzzle:
there cannot be the least doubt in the world that it has been written by two persons doing alternate words. When I draw your attention to the strong t's of 'at' and 'to', and ask you to compare them with the weak ones of 'quarter' and 'twelve,' you will instantly recognize the fact. A very brief analysis of these four words would enable you to say with the utmost confidence that the 'learn' and the 'maybe' are written in the stronger hand, and the 'what' in the weaker…Obviously the business was a bad one, and one of the men who distrusted the other was determined that, whatever was done, each should have an equal hand in it. Now, of the two men, it is clear that the one who wrote the 'at' and 'to' was the ringleader…We might deduce it from the mere character of the one hand as compared with the other. But we have more assured reasons than that for supposing it. If you examine this scrap with attention you will come to the conclusion that the man with the stronger hand wrote all his words first, leaving blanks for the other to fill up. These blanks were not always sufficient, and you can see that the second man had a squeeze to fit his 'quarter' in between the 'at' and the 'to,' showing that the latter were already written. The man who wrote all his words first in undoubtedly the man who planned the affair…You may not be aware that the deduction of a man's age from his writing is one which has brought to considerable accuracy by experts. In normal cases one can place a man in his true decade with tolerable confidence. I say normal cases, because ill-health and physical weakness reproduce the signs of old age, even when the invalid is a youth. In this case, looking at the bold, strong hand of the one, and the rather broken-backed appearance of the other, which still retains its legibility although the t's have begun to lose their crossing, we can say that the one was a young man and the other was advanced in years without being positively decrepit…There is a further point, however, which is subtler and of greater interest. There is something in common between these hands. They belong to men who are blood-relatives. It may be most obvious to you in the Greek e's, but to me there are many small points which indicate the same thing. I have no doubt at all that a family mannerism can be traced in these two specimens of writing. I am only, of course, giving you the leading results now of my examination of the paper. There were twenty-three other deductions which would be of more interest to experts than to you. They all tend to deepen the impression upon my mind that the Cunninghams, father and son, had written this letter.”

Percy Phelp’s Letter in the Naval Treaty:
"And yet the writing is of interest.”
"But the writing is not his own.”
"Precisely. It is a woman's.”
"A man's surely," I cried.
"No, a woman's, and a woman of rare character. You see, at the commencement of an investigation it is something to know that your client is in close contact with some one who, for good or evil, has an exceptional nature.


Tracks outside in the mud:
"There has been murder done, and the murderer was a man. He was more than six feet high, was in the prime of life, had small feet for his height, wore coarse, square-toed boots and smoked a Trichinopoly cigar. He came here with his victim in a four-wheeled cab, which was drawn by a horse with three old shoes and one new one on his off fore leg. In all probability the murderer had a florid face, and the finger-nails of his right hand were remarkably long."
"The very first thing which I observed on arriving there was that a cab had made two ruts with its wheels close to the curb. Now, up to last night, we have had no rain for a week, so that those wheels which left such a deep impression must have been there during the night. There were the marks of the horse's hoofs, too, the outline of one of which was far more clearly cut than that of the other three, showing that that was a new shoe. Since the cab was there after the rain began, and was not there at any time during the morning—I have Gregson's word for that—it follows that it must have been there during the night, and, therefore, that it brought those two individuals to the house.

Room and window outside of the Sholto Murder:
In the first place, how did these folk come, and how did they go? The door has not been opened since last night. How of the window?" He carried the lamp across to it, muttering his observations aloud the while, but addressing them to himself rather than to me. "Window is snibbed on the inner side. Framework is solid. No hinges at the side. Let us open it. No water-pipe near. Roof quite out of reach. Yet a man has mounted by the window. It rained a little last night. Here is the print of a foot in mould upon the sill. And here is a circular muddy mark, and here again upon the floor, and here again by the table. See here, Watson! This is really a very pretty demonstration."
"This is not a footmark," said I.
"It is something much more valuable to us. It is the impression of a wooden stump. You see here on the sill is the boot-mark, a heavy boot with the broad metal heel, and beside it is the mark of the timber-toe."
"It is the wooden-legged man."
"...our wooden-legged friend, though a fair climber, was not a professional sailor. His hands were far from horny. My lens discloses more than one blood-mark, especially towards the end of the rope, from which I gather that he slipped down with such velocity that he took the skin off his hand."

Further Deductions:
His name, I have every reason to believe, is Jonathan Small. He is a poorly-educated man, small, active, with his right leg off, and wearing a wooden stump which is worn away upon the inner side. His left boot has a coarse, square-toed sole, with an iron band round the heel. He is a middle-aged man, much sunburned, and has been a convict. These few indications may be of some assistance to you, coupled with the fact that there is a good deal of skin missing from the palm of his hand.

On the pygmy prints next to them:
"I wish you particularly to notice these footmarks," he said. "Do you observe anything noteworthy about them?"
"They belong," I said, "to a child or a small woman."
"Apart from their size, though. Is there nothing else?"
"They appear to be much as other footmarks."
"Not at all. Look here! This is the print of a right foot in the dust. Now I make one with my naked foot beside it. What is the chief difference?"
"Your toes are all cramped together. The other print has each toe distinctly divided."

Tracks in the snow in Beryl Coronet:
"When I arrived at the house," continued Holmes, "I at once went very carefully round it to observe if there were any traces in the snow which might help me. I knew that none had fallen since the evening before, and also that there had been a strong frost to preserve impressions. I passed along the tradesmen's path, but found it all trampled down and indistinguishable. Just beyond it, however, at the far side of the kitchen door, a woman had stood and talked with a man, whose round impressions on one side showed that he had a wooden leg. I could even tell that they had been disturbed, for the woman had run back swiftly to the door, as was shown by the deep toe and light heel marks, while Wooden-leg had waited a little, and then had gone away. I thought at the time that this might be the maid and her sweetheart, of whom you had already spoken to me, and inquiry showed it was so. I passed round the garden without seeing anything more than random tracks, which I took to be the police; but when I got into the stable lane a very long and complex story was written in the snow in front of me.
"There was a double line of tracks of a booted man, and a second double line which I saw with delight belonged to a man with naked feet. I was at once convinced from what you had told me that the latter was your son. The first had walked both ways, but the other had run swiftly, and as his tread was marked in places over the depression of the boot, it was obvious that he had passed after the other. I followed them up and found they led to the hall window, where Boots had worn all the snow away while waiting. Then I walked to the other end, which was a hundred yards or more down the lane. I saw where Boots had faced round, where the snow was cut up as though there had been a struggle, and, finally, where a few drops of blood had fallen, to show me that I was not mistaken. Boots had then run down the lane, and another little smudge of blood showed that it was he who had been hurt. When he came to the highroad at the other end, I found that the pavement had been cleared, so there was an end to that clew.
"On entering the house, however, I examined, as you remember, the sill and framework of the hall window with my lens, and I could at once see that someone had passed out. I could distinguish the outline of an instep where the wet foot had been placed in coming in. I was then beginning to be able to form an opinion as to what had occurred. A man had waited outside the window; someone had brought the gems; the deed had been overseen by your son; he had pursued the thief; had struggled with him; they had each tugged at the coronet, their united strength causing injuries which neither alone could have effected. He had returned with the prize, but had left a fragment in the grasp of his opponent."

Tracks in Crooked Man:
- He had apparently rushed across the lawn, for his toe-marks were much deeper than his heels
- Here are four prints where the beast has been standing motionless. You see that it is no less than fifteen inches from fore-foot to hind. Add to that the length of neck and head, and you get a creature not much less than two feet long--probably more if there is any tail. But now observe this other measurement. The animal has been moving, and we have the length of its stride. In each case it is only about three inches. You have an indication, you see, of a long body with very short legs attached to it. It has not been considerate enough to leave any of its hair behind it. But its general shape must be what I have indicated, and it can run up a curtain, and it is carnivorous…A canary's cage was hanging in the window, and its aim seems to have been to get at the bird.”

Tracks in the Resident Patient:
I was soon able to corroborate the doctor's tale. This young man has left prints upon the stair-carpet which made it quite superfluous for me to ask to see those which he had made in the room. When I tell you that his shoes were square-toed instead of being pointed like Blessington's, and were quite an inch and a third longer than the doctor's, you will acknowledge that there can be no doubt as to his individuality.

The Lack of Tracks in The Naval Treaty:
But if Mr. Phelps is correct in stating that there is no hiding-place either in the room or the corridors, then the person must have come from outside. If he came from outside on so wet a night, and yet left no trace of damp upon the linoleum, which was examined within a few minutes of his passing, then it is exceeding probably that he came in a cab. Yes, I think that we may safely deduce a cab.

Following the Tracks of the Burgler in The Naval Treaty:
The plump young man led us to a spot where the top of one of the wooden rails had been cracked. A small fragment of the wood was hanging down. Holmes pulled it off and examined it critically.
"Do you think that was done last night? It looks rather old, does it not?”
"Well, possibly so.”
"There are no marks of any one jumping down upon the other side. No, I fancy we shall get no help here.”

Cigar Ashes:
I gathered up some scattered ash from the floor. It was dark in colour and flakey—such an ash as is only made by a Trichinopoly
Sir Charles had evidently stood there for five or ten minutes...Because the ash had twice dropped from his cigar.
To the trained eye there is as much difference between the black ash of a Trichinopoly and the white fluff of bird's-eye as there is between a cabbage and a potato.
I found the ash of a cigar, which my special knowledge of tobacco ashes enables me to pronounce as an Indian cigar. I have, as you know, devoted some attention to this, and written a little monograph on the ashes of 140 different varieties of pipe, cigar, and cigarette tobacco. Having found the ash, I then looked round and discovered the stump among the moss where he had tossed it. It was an Indian cigar, of the variety which are rolled in Rotterdam.”
"And the cigar-holder?”
"I could see that the end had not been in his mouth. Therefore he used a holder. The tip had been cut off, not bitten off, but the cut was not a clean one, so I deduced a blunt pen-knife.”
You still smoke the Arcadia mixture of your bachelor days then! There's no mistaking that fluffy ash upon your coat.
It must have lasted for some time, for it was then that these cigars were smoke. The older man sat in that wicker chair; it was he who used the cigar-holder. The younger man sat over yonder; he knocked his ash off against the chest of drawers.

Cigarettes from Blessington’s room in The Resident Patient:
Seems to have smoked heavily during the night, too. Here are four cigar-ends that I picked out of the fireplace.”
"Hum!" said Holmes, "have you got his cigar-holder?”
"No, I have seen none.”
"His cigar-case, then?”
"Yes, it was in his coat-pocket.”
Holmes opened it and smelled the single cigar which it contained.
"Oh, this is an Havana, and these others are cigars of the peculiar sort which are imported by the Dutch from their East Indian colonies. They are usually wrapped in straw, you know, and are thinner for their length than any other brand." He picked up the four ends and examined them with his pocket-lens.
"Two of these have been smoked from a holder and two without," said he. "Two have been cut by a not very sharp knife, and two have had the ends bitten off by a set of excellent teeth.


The height of a man, in nine cases out of ten, can be told from the length of his stride
When a man writes on a wall, his instinct leads him to write about the level of his own eyes.
Age: If a man can stride four and a-half feet without the smallest effort, he can't be quite in the sere and yellow. That was the breadth of a puddle on the garden walk which he had evidently walked across. Patent-leather boots had gone round, and Square-toes had hopped over.
Hat: label by John Underwood and Sons, 129, Camberwell Road - in order to get the address from the sales clerk

A Few Examples of Long Chains of Reasoning:

Full Chain of Deductions from Holmes examination in the ‘A Study in Scarlet’:
[I could tell] it was a cab and not a private carriage by the narrow gauge of the wheels. The ordinary London growler is considerably less wide than a gentleman's brougham.
I saw also the track of the two men who had first passed through the garden. It was easy to tell that they had been before the others, because in places their marks had been entirely obliterated by the others coming upon the top of them.
the other fashionably dressed, to judge from the small and elegant impression left by his boots
Men who die from heart disease, or any sudden natural cause, never by any chance exhibit agitation upon their features. Having sniffed the dead man's lips I detected a slightly sour smell, and I came to the conclusion that he had had poison forced upon him. Again, I argued that it had been forced upon him from the hatred and fear expressed upon his face.
And now came the great question as to the reason why. Robbery had not been the object of the murder, for nothing was taken. Was it politics, then, or was it a woman? That was the question which confronted me. I was inclined from the first to the latter supposition. Political assassins are only too glad to do their work and to fly. This murder had, on the contrary, been done most deliberately, and the perpetrator had left his tracks all over the room, showing that he had been there all the time. It must have been a private wrong, and not a political one, which called for such a methodical revenge.
When the ring was found, however, it settled the question. Clearly the murderer had used it to remind his victim of some dead or absent woman.
I had already determined in my own mind that the man who had walked into the house with Drebber, was none other than the man who had driven the cab. The marks in the road showed me that the horse had wandered on in a way which would have been impossible had there been anyone in charge of it. Where, then, could the driver be, unless he were inside the house? Again, it is absurd to suppose that any sane man would carry out a deliberate crime under the very eyes, as it were, of a third person, who was sure to betray him. Lastly, supposing one man wished to dog another through London, what better means could he adopt than to turn cabdriver. All these considerations led me to the irresistible conclusion that Jefferson Hope was to be found among the jarveys of the Metropolis.
"What did you go into the pool for...That left foot of yours with its inward twist is all over the place."
These are young McCarthy's feet. Twice he was walking, and once he ran swiftly, so that the soles are deeply marked and the heels hardly visible. That bears out his story. He ran when he saw his father on the ground. Then here are the father's feet as he paced up and down. What is this, then? It is the butt-end of the gun as the son stood listening. And this? Ha, ha! What have we here? Tiptoes! tiptoes! Square, too, quite unusual boots!
...the stone which he had picked up in the wood "This may interest you...The murder was done with it.”
"I see no marks.”
"There are none...The grass was growing under it. It had only lain there a few days. There was no sign of a place whence it had been taken. It corresponds with the injuries. There is no sign of any other weapon.”
"And the murderer?”
"Is a tall man, left-handed, limps with the right leg, wears thick-soled shooting-boots and a gray cloak, smokes Indian cigars, uses a cigar-holder, and carries a blunt pen-knife in his pocket.
But his lameness?”
"The impression of his right foot was always less distinct than his left. He put less weight upon it. Why? Because he limped--he was lame.”
"But his left-handedness.”
"You were yourself struck by the nature of the injury as recorded by the surgeon at the inquest. The blow was struck from immediately behind, and yet was upon the left side. Now, how can that be unless it were by a left-handed man? He had stood behind that tree during the interview between the father and son. He had even smoked there. I found the ash of a cigar, which my special knowledge of tobacco ashes enables me to pronounce as an Indian cigar....Having found the ash, I then looked round and discovered the stump among the moss where he had tossed it. It was an Indian cigar, of the variety which are rolled in Rotterdam.”
"And the cigar-holder?”
"I could see that the end had not been in his mouth. Therefore he used a holder. The tip had been cut off, not bitten off, but the cut was not a clean one, so I deduced a blunt pen-knife.”

Reading Watson’s Mind in The Resident Patient:
Finding that Holmes was too absorbed for conversation, I had tossed aside the barren paper, and leaning back in my chair, I fell into a brown study. Suddenly my companion's voice broke in upon my thoughts.
"You are right, Watson," said he. "It does seem a very preposterous way of settling a dispute.”
"Most preposterous!" I exclaimed, and then, suddenly realizing how he had echoed the inmost thought of my soul, I sat up in my chair and stared at him in blank amazement.
"What is this, Holmes?" I cried. "This is beyond anything which I could have imagined.”
He laughed heartily at my perplexity.
"You remember," said he, "that some little time ago, when I read you the passage in one of Poe's sketches, in which a close reasoner follows the unspoken thought of his companion, you were inclined to treat the matter as a mere tour de force of the author. On my remarking that I was constantly in the habit of doing the same thing you expressed incredulity.”
"Oh, no!”
"Perhaps not with your tongue, my dear Watson, but certainly with your eyebrows. So when I saw you throw down your paper and enter upon a train of thought, I was very happy to have the opportunity of reading it off, and eventually of breaking into it, as a proof that I had been in rapport with you.”
But I was still far from satisfied. "In the example which you read to me," said I, "the reasoner drew his conclusions from the actions of the man whom he observed. If I remember right, he stumbled over a heap of stones, looked up at the stars, and so on. But I have been seated quietly in my chair, and what clews can I have given you?”
"You do yourself an injustice. The features are given to man as the means by which he shall express his emotions, and yours are faithful servants.”
"Do you mean to say that you read my train of thoughts from my features?”
"Your features, and especially your eyes. Perhaps you cannot yourself recall how your reverie commenced?”
"No, I cannot.”
"Then I will tell you. After throwing down your paper, which was the action which drew my attention to you, you sat for half a minute with a vacant expression. Then your eyes fixed themselves upon your newly-framed picture of General Gordon, and I saw by the alteration in your face that a train of thought had been started. But it did not lead very far. Your eyes turned across to the unframed portrait of Henry Ward Beecher which stands upon the top of your books. You then glanced up at the wall, and of course your meaning was obvious. You were thinking that if the portrait were framed it would just cover that bare space and correspond with Gordon's picture over there.”
"You have followed me wonderfully!" I exclaimed.
"So far I could hardly have gone astray. But now your thoughts went back to Beecher, and you looked hard across as if you were studying the character in his features. Then your eyes ceased to pucker, but you continued to look across, and your face was thoughtful. You were recalling the incidents of Beecher's career. I was well aware that you could not do this without thinking of the mission which he undertook on behalf of the North at the time of the Civil War, for I remember you expressing your passionate indignation at the way in which he was received by the more turbulent of our people. You felt so strongly about it that I knew you could not think of Beecher without thinking of that also. When a moment later I saw your eyes wander away from the picture, I suspected that your mind had now turned to the Civil War, and when I observed that your lips set, your eyes sparkled, and your hands clinched, I was positive that you were indeed thinking of the gallantry which was shown by both sides in that desperate struggle. But then, again, your face grew sadder; you shook your head. You were dwelling upon the sadness and horror and useless waste of life. Your hand stole towards your own old wound, and a smile quivered on your lips, which showed me that the ridiculous side of this method of settling international questions had forced itself upon your mind. At this point I agreed with you that it was preposterous, and was glad to find that all my deductions had been correct.”

Full Chain of Logic from Naval Treaty:
Holmes: “I had already begun to suspect Joseph, from the fact that you had intended to travel home with him that night, and that therefore it was a likely enough thing that he should call for you, knowing the Foreign Office well, upon his way. When I heard that some one had been so anxious to get into the bedroom, in which no one but Joseph could have concealed anything--you told us in your narrative how you had turned Joseph out when you arrived with the doctor--my suspicions all changed to certainties, especially as the attempt was made on the first night upon which the nurse was absent, showing that the intruder was well acquainted with the ways of the house.”
"How blind I have been!”
"The facts of the case, as far as I have worked them out, are these: this Joseph Harrison entered the office through the Charles Street door, and knowing his way he walked straight into your room the instant after you left it. Finding no one there he promptly rang the bell, and at the instant that he did so his eyes caught the paper upon the table. A glance showed him that chance had put in his way a State document of immense value, and in an instant he had thrust it into his pocket and was gone. A few minutes elapsed, as you remember, before the sleepy commissionnaire drew your attention to the bell, and those were just enough to give the thief time to make his escape.”

Some of Holmes' Choisest Axioms:
·                 By a man's finger nails, by his coat-sleeve, by his boot, by his trouser knees, by the callosities of his forefinger and thumb, by his expression, by his shirt cuffs—by each of these things a man's calling is plainly revealed. That all united should fail to enlighten the competent enquirer in any case is almost inconceivable.
·                 I have already explained to you that what is out of the common is usually a guide rather than a hindrance.
·                 It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.
·                 What do the public, the great unobservant public, who could hardly tell a weaver by his tooth or a compositor by his left thumb, care about the finer shades of analysis and deduction!
·                 "To the curious incident of the dog in the night-time.” / "The dog did nothing in the night-time.” / "That was the curious incident," remarked Sherlock Holmes.
·                 It is of the highest importance in the art of detection to be able to recognize, out of a number of facts, which are incidental and which vital. Otherwise your energy and attention must be dissipated instead of being concentrated.
·                 I make a point of never having any prejudices, and of following docilely wherever fact may lead me.
·                 You should consider your brain originally is like a little empty attic, and you have to stock it with furniture as you choose. A fool takes in all lumber of every sort that he comes across, so that the knowledge which might be useful to him gets crowded out, or at best is jumbled up with a lot of other things, so that he has difficulty in laying his hands upon it. Now the skilled workman is very careful indeed as to what he takes into his brain attic. He will have nothing but the tools which may help him in doing his work, but of these he has a large assortment and all in the most perfect order. It is a mistake to think that that a little room has elastic walls and can distend to any extent. Depend upon it there comes a time when for every addition of knowledge you forgot something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones.
·                 An observant man can learn by an accurate and systematic examination of all that came in his way. From a drop of water, a logician could infer the possibility of an Atlantic or a Niagara without having seen or heard of one or the other. So all life is a great chain, the nature of which is known whenever we are shown a single link of it.
·                 Always approach a case with an absolutely blank mind, which is always an advantage. Form no theories, just simply observe and draw inferences from your observations.
·                 The temptation to form premature theories upon insufficient data is the bane of this profession.
·                 They say that genius is an infinite capacity for taking pains. It’s a very bad definition, but it does apply to detective work.
·                 To a great mind, nothing is little.
·                 It is a mistake to confound strangeness with mystery. The most commonplace crime is often the most mysterious, because it presents no new or special features from which deductions may be drawn.
·                 There is nothing new under the sun. It has all been done before.
·                 Often what is out of the common is usually a guide rather than a hindrance. In solving a problem of this sort, the grand thing is to be able to reason backward. That is a very useful accomplishment, and a very easy one, but people do not practice it much. In the everyday affairs of life it is more useful to reason forward, and so the other comes to be neglected. Most people, if you describe a train of events to them, will tell you what the results would be. They can put those events together in their minds, and argue from them that something will come to pass. There are a few people, however, who, if you told them a result, would be able to evolve from their own inner consciousness what the steps were which led up to that result. This power is what I mean when I talk of reasoning backward, or analytically.
·                 There is no branch of detective science which is so important and so much neglected as the art of tracing footsteps. Always lay great stress upon it, and practice it till it becomes second nature.
·                 Detection is, or ought to be, an exact science and should be treated in the same cold and unemotional manner.
·                 Never guess. It is a shocking habit – destructive to the logical faculty. Observe the small facts upon which large inferences may depend.
·                 When you have eliminated the impossible, whatever remains, however improbable, must be the truth.
·                 The main thing with people when you talk to them in an investigation is to never let them know that their information can be of the slightest importance to you. If you do they will instantly shut up like an oyster. If you listen to them under protest, as it were, you are very likely to get what you want.
·                 Women are never to be entirely trusted – not the best of them.
·                 It is good to adopt a system of docketing all paragraphs concerning men and things, so that it would be difficult to name a subject or a person on which one could not at once furnish information.
·                 Often the strangest and most unique things are very often connected not with the larger but with the smaller crimes, and occasionally, indeed, where there is room for doubt whether any positive crime has been committed.
·                 As a rule, the most bizarre a thing is the less mysterious it proves to be. It is your commonplace, featureless crimes which are really puzzling, just as a commonplace face is the most difficult to identify.
·                 Usually in unimportant matters there is a field for the observation, and for the quick analysis of cause and effect which gives the charm to the investigation. The larger crimes are apt to be the simpler, for the bigger the crime the more obvious, as a rule, is the motive.
·                 It should be your business to know things. To train yourself to see what others overlook.
·                 In an investigation, the little things are infinitely the most important.
·                 Never trust to general impressions, but concentrate yourself upon details. On examining a woman’s appearance, you should realize the importance of sleeves, the suggestiveness of thumb-nails, or the great issues that may hang from a boot-lace. In a man it is perhaps better first to take the knee of the trouser.
·                 Singularity is almost invariably a clue. The more featureless and commonplace a crime is, the more difficult it is to bring it home.
·                 The most difficult crime to track is the one which is purposeless.
·                 Depend on it, there is nothing so unnatural as the commonplace.
·                 You must look for consistency. Where there is a want of it you must suspect deception.
·                 Your eyes should be trained to examine faces and not their trimmings. It is the first quality of a criminal investigation that you should see through a disguise.
·                 Circumstantial evidence is a very tricky thing. It may seem to point very straight to one thing, but if you shift your own point of view a little, you may find it pointing in an equally uncompromising manner to something entirely different.
·                 Your method should be founded upon the observation of trifles.
·                 The ideal reason would, when one had been shown a single fact in all its bearings, deduce from it not only all the chain of events which led up to it but also all the results which would follow from it. As Cuvier could correctly describe a whole animal by the contemplation of a single bone, so the observer who has thoroughly understood one link in a series of incidents should be able to accurately state all the other ones, both before and after. We have not yet grasped the results which the reason alone can attain to. Problems may be solved in the study which have baffled all those who have sought a solution by the aid of the senses. To carry the art, however, to its highest pitch, it is necessary that the reasoner should be able to utilize all the facts which have come to his knowledge; and this in itself implies, as you will readily see, a possession of all knowledge, which, even in these days of free education and encyclopedias, is a somewhat rare accomplishment. It is not impossible, however, that a man should possess all knowledge which is likely to be useful to him in his work. A man should keep his little brain-attic stocked with all the furniture that he is likely to use, and the rest he can put away in the lumber-room of his library, where he can get it if he wants it.
·                 Often the impression of a woman may be more valuable than the conclusion of an analytical reasoner.
·                 Read nothing but the criminal news and the agony column. The latter is always instructive.
·                 The most practical thing that you ever can do in your life would be to shut yourself up for three months and read twelve hours a day at the annals of crime. Everything comes in circles. The old wheel turns, and the same spoke comes up. It’s all been done before, and will be again. Then when you have heard some slight indication of the course of events in an investigation, you should be able to guide yourself by the thousands of other similar cases which should occur to your memory.
·                 An investigator should look at everything with reference to his own special subject. One, for example, can see some scattered houses along a countryside, and become impressed by their beauty. But to the investigator, the only thought sometimes should be a feeling of their isolation and the impunity with which crime may be committed there.
·                 Crime is common. Logic is rare. Therefore it is upon logic rather than upon crime that you should dwell.
·                 Pipes are occasionally of extraordinary interest. Nothing has more individuality, save perhaps watches and bootlaces.
·                 Always in an investigation you should put yourself in the man’s place, and, having first gauged his intelligence, try to imagine how you would proceed under the same circumstances.
·                 Results are come by always putting yourself in the other fellow’s place, and thinking what you would do yourself. It takes some imagination, but it pays.
·                 It is of the highest importance in the art of detection to be able to recognize, out of a number of facts, which are incidental and which vital. Otherwise your energy and attention must be dissipated instead of being concentrated.
·                 In an investigation, it is only the colourless, uneventful cases which are hopeless.
·                 In an investigation, always look for a possible alternative, and provide against it. It is the first rule of criminal investigations.
·                 The features given to man are means by which he shall express his emotions, and you can read a man’s train of thought from his features, especially his eyes.
·                 As long as the criminal remains upon two legs so must there be some indentation, some abrasion, some trifling displacement which can be detected by the scientific searcher.
·                 One characteristic that the detective should have in the Science of Deduction and Analysis is the ability to throw the brain out of action and to switch all thoughts on to lighter things wherever you think things could no longer work to advantage.
·                 Education never ends. It is a series of lessons with the greatest for the last.
·                 First real insight into the character of parents is gained by studying their children.
·                 Your thoughts about dogs should be analogous. A dog always reflects the family life. Whoever saw a frisky dog in a gloomy family, or a sad dog in a happy one? Snarling people have snarling dogs, dangerous people have dangerous ones. And their passing moods may reflect the passing moods of others.
·                 When a doctor does go wrong he is the first of criminals. He has the nerve and he has the knowledge.
·                 When you follow two separate chains of thought, you will find some point of intersection which should approximate to the truth.
·                 Do not agree with those who rank modesty among the virtues. To the logician all things should be seen exactly as they are, and to underestimate one’s self is as much a departure from the truth as to exaggerate one’s own powers.
·                 It is always good to have someone with you on whom you can thoroughly rely. Local aid is always either worthless or else biased.
·                 It is my belief, founded upon experience, that the lowest and vilest alleys do not present a more dreadful record of sin than does the smiling and beautiful countryside.

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