THE SCIENCE OF DEDUCTION
SHERLOCK HOLMES took his bottle from the corner of the
mantelpiece, and his hypodermic syringe from its neat morocco case. With his long, white,
nervous fingers he adjusted the delicate needle and rolled back his left shirtcuff. For
some little time his eyes rested thoughtfully upon the sinewy forearm and wrist, all
dotted and scarred with innumerable puncture-marks. Finally, he thrust the sharp point
home, pressed down the tiny piston, and sank back into the velvet-lined armchair with a
long sigh of satisfaction.
Three times a day for many months I had witnessed this
performance, but custom had not reconciled my mind to it. On the contrary, from day to day
I had become more irritable at the sight, and my conscience swelled nightly within me at
the thought that I had lacked the courage to protest. Again and again I had registered a
vow that I should deliver my soul upon the subject; but there was that in the cool,
nonchalant air of my companion which made him the last man with whom one would care to
take anything approaching to a liberty. His great powers, his masterly manner, and the
experience which I had had of his many extraordinary qualities, all made me diffident and
backward in crossing him.
Yet upon that afternoon, whether it was the Beaune which I had
taken with my lunch or the additional exasperation produced by the extreme deliberation of
his manner, I suddenly felt that I could hold out no longer.
Which is it to-day, I asked, morphine or
He raised his eyes languidly from the old black-letter volume
which he had opened.
It is cocaine, he said, a seven-per-cent
solution. Would you care to try it?
No, indeed, I answered brusquely. My
constitution has not got over the Afghan campaign yet. I cannot afford to throw any extra
strain upon it.
He smiled at my vehemence. Perhaps you are right,
Watson, he said. I suppose that its influence is physically a bad one. I find
it, however, so transcendently stimulating and clarifying to the mind that its secondary
action is a matter of small moment.
But consider! I said earnestly. Count the
cost! Your brain may, as you say, be roused and excited, but it is a pathological and
morbid process which involves increased tissue-change and may at least leave a permanent
weakness. You know, too, what a black reaction comes upon you. Surely the game is hardly
worth the candle. Why should you, for a mere passing pleasure, risk the loss of those
great powers with which you have been endowed? Remember that I speak not only as one
comrade to another but as a medical man to one for whose constitution he is to some extent
He did not seem offended. On the contrary, he put his
finger-tips together, and leaned his elbows on the arms of his chair, like one who has a
relish for conversation.
My mind, he said, rebels at stagnation. Give
me problems, give me work, 
give me the most abstruse cryptogram, or the most intricate analysis, and I am in my own
proper atmosphere. I can dispense then with artificial stimulants. But I abhor the dull
routine of existence. I crave for mental exaltation. That is why I have chosen my own
particular profession, or rather created it, for I am the only one in the world.
The only unofficial detective? I said, raising my
The only unofficial consulting detective, he
answered. I am the last and highest court of appeal in detection. When Gregson, or
Lestrade, or Athelney Jones are out of their depthswhich, by the way, is their
normal statethe matter is laid before me. I examine the data, as an expert, and
pronounce a specialists opinion. I claim no credit in such cases. My name figures in
no newspaper. The work itself, the pleasure of finding a field for my peculiar powers, is
my highest reward. But you have yourself had some experience of my methods of work in the
Jefferson Hope case.
Yes, indeed, said I cordially. I was never
so struck by anything in my life. I even embodied it in a small brochure, with the
somewhat fantastic title of A Study in Scarlet.
He shook his head sadly.
I glanced over it, said he. Honestly, I
cannot congratulate you upon it. Detection is, or ought to be, an exact science and should
be treated in the same cold and unemotional manner. You have attempted to tinge it with
romanticism, which produces much the same effect as if you worked a love-story or an
elopement into the fifth proposition of Euclid.
But the romance was there, I remonstrated. I
could not tamper with the facts.
Some facts should be suppressed, or, at least, a just
sense of proportion should be observed in treating them. The only point in the case which
deserved mention was the curious analytical reasoning from effects to causes, by which I
succeeded in unravelling it.
I was annoyed at this criticism of a work which had been
specially designed to please him. I confess, too, that I was irritated by the egotism
which seemed to demand that every line of my pamphlet should be devoted to his own special
doings. More than once during the years that I had lived with him in Baker Street I had
observed that a small vanity underlay my companions quiet and didactic manner. I
made no remark, however, but sat nursing my wounded leg. I had had a Jezail bullet through
it some time before, and though it did not prevent me from walking it ached wearily at
every change of the weather.
My practice has extended recently to the
Continent, said Holmes after a while, filling up his old brier-root pipe. I
was consulted last week by Francois le Villard, who, as you probably know, has come rather
to the front lately in the French detective service. He has all the Celtic power of quick
intuition, but he is deficient in the wide range of exact knowledge which is essential to
the higher developments of his art. The case was concerned with a will and possessed some
features of interest. I was able to refer him to two parallel cases, the one at Riga in
1857, and the other at St. Louis in 1871, which have suggested to him the true solution.
Here is the letter which I had this morning acknowledging my assistance.
He tossed over, as he spoke, a crumpled sheet of foreign
notepaper. I glanced my eyes down it, catching a profusion of notes of admiration, with
stray magnifiques, 
coup-de-maîtres and tours-de-force, all testifying to the ardent
admiration of the Frenchman.
He speaks as a pupil to his master, said I.
Oh, he rates my assistance too highly, said
Sherlock Holmes lightly. He has considerable gifts himself. He possesses two out of
the three qualities necessary for the ideal detective. He has the power of observation and
that of deduction. He is only wanting in knowledge, and that may come in time. He is now
translating my small works into French.
Oh, didnt you know? he cried, laughing.
Yes, I have been guilty of several monographs. They are all upon technical subjects.
Here, for example, is one Upon the Distinction between the Ashes of the Various
Tobaccos. In it I enumerate a hundred and forty forms of cigar, cigarette, and pipe
tobacco, with coloured plates illustrating the difference in the ash. It is a point which
is continually turning up in criminal trials, and which is sometimes of supreme importance
as a clue. If you can say definitely, for example, that some murder had been done by a man
who was smoking an Indian lunkah, it obviously narrows your field of search. To
the trained eye there is as much difference between the black ash of a Trichinopoly and
the white fluff of birds-eye as there is between a cabbage and a potato.
You have an extraordinary genius for minutiae, I
I appreciate their importance. Here is my monograph upon
the tracing of footsteps, with some remarks upon the uses of plaster of Paris as a
preserver of impresses. Here, too, is a curious little work upon the influence of a trade
upon the form of the hand, with lithotypes of the hands of slaters, sailors, cork-cutters,
compositors, weavers, and diamond-polishers. That is a matter of great practical interest
to the scientific detectiveespecially in cases of unclaimed bodies, or in
discovering the antecedents of criminals. But I weary you with my hobby.
Not at all, I answered earnestly. It is of
the greatest interest to me, especially since I have had the opportunity of observing your
practical application of it. But you spoke just now of observation and deduction. Surely
the one to some extent implies the other.
Why, hardly, he answered, leaning back luxuriously
in his armchair and sending up thick blue wreaths from his pipe. For example,
observation shows me that you have been to the Wigmore Street Post-Office this morning,
but deduction lets me know that when there you dispatched a telegram.
Right! said I. Right on both points! But I
confess that I dont see how you arrived at it. It was a sudden impulse upon my part,
and I have mentioned it to no one.
It is simplicity itself, he remarked, chuckling at
my surpriseso absurdly simple that an explanation is superfluous; and yet it
may serve to define the limits of observation and of deduction. Observation tells me that
you have a little reddish mould adhering to your instep. Just opposite the Wigmore 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 neighbourhood. So much
is observation. The rest is deduction.
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 postcards. 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.
In this case it certainly is so, I replied after a
little thought. The thing, however, is, as you say, of the simplest. Would you think
me impertinent if I were to put your theories to a more severe test?
On the contrary, he answered, it would
prevent me from taking a second dose of cocaine. I should be delighted to look into any
problem which you might submit to me.
I have heard you say it is difficult for a man to have
any object in daily use without leaving the impress of his individuality upon it in such a
way that a trained observer might read it. Now, I have here a watch which has recently
come into my possession. Would you have the kindness to let me have an opinion upon the
character or habits of the late owner?
I handed him over the watch with some slight feeling of
amusement in my heart, for the test was, as I thought, an impossible one, and I intended
it as a lesson against the somewhat dogmatic tone which he occasionally assumed. He
balanced the watch in his hand, gazed hard at the dial, opened the back, and examined the
works, first with his naked eyes and then with a powerful convex lens. I could hardly keep
from smiling at his crestfallen face when he finally snapped the case to and handed it