THE SCIENCE OF DEDUCTION.
SHERLOCK HOLMES took his bottle from the corner of the
mantel-piece 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
shirt-cuff. 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 arm-chair 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 cocaine?"
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 last 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 answerable."
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 only unofficial detective?" I said, raising my eyebrows.
"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
depths -- which, by the way, is their normal state -- the
matter is laid before me. I examine the data, as an expert,
and pronounce a specialist's 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 companion's 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 François 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 note-paper. I glanced my
eyes down it, catching a profusion of notes of admiration,
with stray "magnifiques", "coup-de-mâitres," 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, didn't 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 Tobaccoes.'
In it I enumerate a hundred and forty forms of cigar-,
cigarette-, and pipe-tobacco, with colored 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 has 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 bird's-eye as there is between a cabbage and
"You have an extraordinary genius for minutiæ," I remarked.
"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 detective, -- especially 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
arm-chair, 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 despatched a telegram."
"Right!" said I. "Right on both points! But I confess that
I don't 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
surprise, -- "so 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 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. 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 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."
"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 that 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 back.
"There are hardly any data," he remarked. "The watch has been
recently cleaned, which robs me of my most suggestive facts."
"You are right," I answered. "It was cleaned before being
sent to me." In my heart I accused my companion of putting
forward a most lame and impotent excuse to cover his failure.
What data could he expect from an uncleaned watch?
"Though unsatisfactory, my research has not been entirely
barren," he observed, staring up at the ceiling with dreamy,
lack-lustre eyes. "Subject to your correction, I should
judge that 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 inquiries 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?"
"It is as clear as daylight," I answered. "I regret the
injustice which I did you. I should have had more faith in
your marvellous faculty. May I ask whether you have any
professional inquiry on foot at present?"
"None. Hence the cocaine. I cannot live without brain-work.
What else is there to live for? Stand at the window here.
Was ever such a dreary, dismal, unprofitable world? See how
the yellow fog swirls down the street and drifts across the
dun-colored houses. What could be more hopelessly prosaic
and material? What is the use of having powers, doctor,
when one has no field upon which to exert them? Crime is
commonplace, existence is commonplace, and no qualities save
those which are commonplace have any function upon earth."
I had opened my mouth to reply to this tirade, when with a
crisp knock our landlady entered, bearing a card upon the
"A young lady for you, sir," she said, addressing my companion.
"Miss Mary Morstan," he read. "Hum! I have no recollection
of the name. Ask the young lady to step up, Mrs. Hudson.
Don't go, doctor. I should prefer that you remain."