How to Think Like Sherlock (8 page)

I knew you came from Afghanistan. From long habit the train of thoughts ran so swiftly through my mind, that I arrived at the conclusion without being conscious of intermediate steps. There were such steps, however. The train of reasoning ran, ‘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.’ The whole train of thought did not occupy a second. I then remarked that you came from Afghanistan, and you were astonished.

Conan Doyle took his inspiration for such deductive brilliance from a real-life source: Dr Joseph Bell. Conan Doyle studied medicine at Edinburgh University under Bell in the 1870s and would later write to tell him, ‘It is certainly to you that I owe Sherlock Holmes… I do not think that his analytical work is in the least an exaggeration of some effects which I have seen you produce in the out-patient ward.’

Bell’s great trick was to diagnose a patient and discern his background without taking any form of history. It was said he could spot a sailor by his rolling gait, a traveller’s route by the tattoos he bore, and any number of occupations from a glimpse at a subject’s hands. As if to prove the point, Conan Doyle once saw him correctly place a patient as a non-commissioned officer, recently discharged from the Highland Regiment posted in Barbados.

In
A Study in Scarlet
, Watson arose one morning to find a magazine on the table of 221B Baker Street. His eye was drawn to one particular article bearing a pencil mark at the heading:

Its somewhat ambitious title was ‘The Book of Life’, and it attempted to show how much an observant man might learn by an accurate and systematic examination of all that came in his way. It struck me as being a remarkable mixture of shrewdness and of absurdity. The reasoning was close and intense, but the deductions appeared to me to be far fetched and exaggerated. The writer claimed by a momentary expression, a twitch of a muscle or a glance of an eye, to fathom a man’s inmost thoughts. Deceit, according to him, was an impossibility in the case of one trained to observation and analysis. His conclusions were as infallible as so many propositions of Euclid. So startling would his results appear to the uninitiated that until they learned the processes by which he had arrived at them they might well consider him as a necromancer.

Watson was initially rather dismissive of its contents, describing it as ‘ineffable twaddle’ and claiming not to have ‘read such rubbish in my life’. A moment or two later, though, Holmes revealed that he himself was the author of the piece. As such, it is invaluable to students of the Great Detective for its explanation of his deductive process:

‘From a drop of water,’ said the writer, ‘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. Like all other arts, the Science of Deduction and Analysis is one which can only be acquired by long and patient study, nor is life long enough to allow any mortal to attain the highest possible perfection in it. Before turning to those moral and mental aspects of the matter which present the greatest difficulties, let the inquirer begin by mastering more elementary problems. Let him, on meeting a fellow-mortal, learn at a glance to distinguish the history of the man, and the trade or profession to which he belongs. Puerile as such an exercise may seem, it sharpens the faculties of observation, and teaches one where to look and what to look for. By a man’s fingernails, by his coat-sleeve, by his boots, by his trouser-knees, by the callosities of his forefinger and thumb, by his expression, by his shirtcuffs – by each of these things a man’s calling is plainly revealed. That all united should fail to enlighten the competent inquirer in any case is almost inconceivable.’

‘Yes; I have a turn both for observation and for deduction,’ Holmes told Watson. ‘The theories which I have expressed there, and which appear to you to be so chimerical, are really extremely practical – so practical that I depend upon them for my bread and cheese.’

Improving Your Deductive Skills

‘“When I hear you give your reasons,” I remarked, “the thing always appears to me to be so ridiculously simple that I could easily do it myself, though at each successive instance of your reasoning I am baffled until you explain your process.”’

‘A SCANDAL IN BOHEMIA’

To improve your own deductive powers, you can do no better than read the entire Sherlock Holmes canon. School yourself in the many incredible examples of deductive reasoning that litter the stories and aim to mirror as many of the master’s techniques as humanly possible. To watch the Great Detective in action is never less than a delight, as Watson himself recalled in
‘
The Adventure of the Speckled Band
’:

I had no keener pleasure than in following Holmes in his professional investigations, and in admiring the rapid deductions, as swift as intuitions, and yet always founded on a logical basis with which he unravelled the problems which were submitted to him.

There are far too many examples to cite here, but virtually anything could serve as useful evidence for Holmes. Here was a man who could discern vast amounts about a suspect from the cigar ash he left scattered at a crime scene, who could calculate a man’s height from the implied stride length provided by a set of footprints, and who could even (in
‘
The Adventure of the Beryl Coronet
’
) unravel ‘a very long and complex story … written in the snow in front of me’.

There are one or two grand set pieces worth analysing in the pursuit of learning Holmes’s secrets.
The Sign of Four
offers up a particularly notable example. Watson hands Holmes a pocket watch and challenges Sherlock to provide ‘an opinion upon the character or habits of the late owner’. Holmes begins by complaining that the watch has recently been cleaned, robbing him of his best evidence. This is, as we might suspect, simply a bit of showmanship on his part.

‘Subject to your correction, I should judge that the watch belonged to your elder brother, who inherited it from your father,’ he begins.

‘That you gather, no doubt, from the H. W. upon the back?’ Watson fires 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. Jewellery 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.’

So far, so logical. But then comes a leap in Holmes’s deductions that at first sight seems beyond reasonable:

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.

Initially, Watson is knocked back on his haunches, distraught that such a painful personal episode has been so casually revealed. He accuses Holmes of being ‘unworthy’, suggesting he had made prior enquiries into his family’s past or else had resorted to guess work. Holmes soon corrects his companion:

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.

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.

What you can’t learn about deduction from the Holmes stories is probably not worth knowing, but here are a few other hints and tips to help: