“It is simplicity itself,” said [Holmes]; “my 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.
I could not help laughing at the ease with which he explained his process of deduction. “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. And yet I believe that my eyes are as good as yours.”Arthur Conan Doyle (1859-1930) British writer and physician
Story (1891-07), “A Scandal in Bohemia,” ch. 1, The Strand Magazine, Vol. 2, No. 1
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Quotations about:
deduction
Note not all quotations have been tagged, so Search may find additional quotes on this topic.
No, no: I never guess. It is a shocking habit, — destructive to the logical faculty.
Arthur Conan Doyle (1859-1930) British writer and physician
Story (1890-02), “The Sign of the Four,” ch. 1 [Holmes], Lippincott’s Monthly Magazine, Vol. 45 (US) / 1 (UK)
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The original publication, and Doyle's manuscript (along with many other iterations across media) use "The Sign of the Four" as the title, while others (including the first book publications) use "The Sign of Four." The five-word form is used most commonly in the story, but the four-word form does show up. (More info.)
Published in novel form as The Sign of Four (1890-10).
It was easier to know it than to explain why I know it. If you were asked to prove that two and two made four, you might find some difficulty, and yet you are quite sure of the fact.
Arthur Conan Doyle (1859-1930) British writer and physician
Story (1886-04), “A Study in Scarlet,” Part 1, ch. 3 [Holmes], Beeton’s Christmas Annual, Vol. 28 (1887-11-21)
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“You appeared to be surprised when I told you, on our first meeting, that you had come from Afghanistan.”
“You were told, no doubt.”
“Nothing of the sort. 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.”Arthur Conan Doyle (1859-1930) British writer and physician
Story (1886-04), “A Study in Scarlet,” Part 1, ch. 2, Beeton’s Christmas Annual, Vol. 28 (1887-11-21)
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Holmes and Watson. Published in novel form 1888-07.
In the Sherlock TV episode 01x01 "A Study in Pink" (w. Steven Moffat) (2010-07-25), this explanation is reworked:HOLMES: When I met you for the first time yesterday, I said "Afghanistan or Iraq?" You looked surprised.
WATSON: How did you know?
HOLMES: I didn't know, I saw. Your haircut, the way you hold yourself, says military. But your conversation as you entered the room said trained at Bart's, so army doctor. Obvious. Your face is tanned, but no tan above the wrists: you've been abroad but not sunbathing. The limp's really bad when you walk, but you don't ask for a chair when you stand, like you've forgotten about it, so it's at least partly psychosomatic. That says the original circumstances of the injury were probably traumatic: wounded in action, then. Wounded in action, suntan: Afghanistan or Iraq.
The same past data can confirm a theory and its exact opposite! If you survive until tomorrow, it could mean that either a) you are more likely to be immortal or b) that you are closer to death. Both conclusions rely on the exact same data.
Nassim Nicholas Taleb (b. 1960) Lebanese-American essayist, statistician, risk analyst, aphorist
The Black Swan, Part 2, ch. 11 “How to Look for Bird Poop” (2007)
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Those long chains composed of very simple and easy reasonings, which geometers customarily use to arrive at their most difficult demonstrations, had given me occasion to suppose that all the things which come within the scope of human knowledge are interconnected in the same way. And I thought that, provided we refrain froma ccepting anything as true which is not, and always keep to the order required for deducing one thing from another, there can be nothing too remote to be reached in the end or too well hidden to be discovered.
[Ces longues chaînes de raisons, toutes simples et faciles, dont les géomètres ont coutume de se servir pour parvenir à leurs plus difficiles démonstrations, m’avoient donné occasion de m’imaginer que toutes les choses qui peuvent tomber sous la connoissance des hommes s’entresuivent en même façon, et que, pourvu seulement qu’on s’abstienne d’en recevoir aucune pour vraie qui ne le soit, et qu’on garde toujours l’ordre qu’il faut pour les déduire les unes des autres, il n’y en peut avoir de si éloignées auxquelles enfin on ne parvienne, ni de si cachées qu’on ne découvre.]
René Descartes (1596-1650) French philosopher, mathematician
Discourse on Method [Discours de la méthode], Part 2 (1637) [tr. Cottingham, Stoothoff (1985)]
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(Source (French)). Alternate translations:Those long chains of reasons, (though simple and easie) which the Geometricians commonly use to lead us to their most difficult demonstrations, gave me occasion to imagine, That all things which may fall under the knowledge of Men, follow one the other in the same manner, and so we doe only abstain from receiving any one for true, which is not so, and observe always the right order of deducing them one from the other, there can be none so remote, to which at last we shall not attain; nor so hid, which we shall not discover.
[Newcombe ed. (1649)]The long chains of simple and easy reasonings by means of which geometers are accustomed to reach the conclusions of their most difficult demonstrations, had led me to imagine that all things, to the knowledge of which man is competent, are mutually connected in the same way, and that there is nothing so far removed from us as to be beyond our reach, or so hidden that we cannot discover it, provided only we abstain from accepting the false for the true, and always preserve in our thoughts the order necessary for the deduction of one truth from another.
[tr. Veitch (1850)]Those long chains of reasoning, simple and easy as they are of which geometricians make use in order to arrive at the most difficult demonstrations, had caused me to imagine that all those things which fall under the cognizance of man might very likely be mutually related in the same fashion; and that, provided only that we abstain from receiving anything as true which is not so, and always retain the order which is necessary in order to deduce the one conclusion from the other, there can be nothing so remote that we cannot reach to it, nor to recondite that we cannot discover it.
[tr. Haldane & Ross (1911)]These long chains of perfectly simple and easy reasonings by means of which geometers are accustomed to carry out their most difficult demonstrations had led me to fancy that everything that can fall under human knowledge forms a similar sequence; and that so long as we avoid accepting as true what it not so, and always preserve the right order for deduction of one thing from another, there can be nothing too remote to be reached in the end, or too well hidden to be discovered.
[tr. Ascombe & Geach (1971)]
Nor let it be feared that erroneous deductions may be made from such recorded facts: the errors which arise from the absence of facts are far more numerous and more durable than those which result from unsound reasoning respecting true data.
Charles Babbage (1791-1871) English mathematician, computer pioneer, philosopher
On the Economy of Machinery and Manufactures, ch. 7 (1832)
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Sometimes paraphrased, "Errors using inadequate data are much less than those using no data at all."
From principles is derived probability, but truth or certainty is obtained only from facts.
Jesse Olney (1798-1872) American geographer, educator, politician
In Godwin, The National Preceptor, Lesson 85 “Select Sentences,” rule #19 (1830)
If a man will begin with certainties, he shall end in doubts; but if he will be content to begin in doubts, he shall end in certainties.
Francis Bacon (1561-1626) English philosopher, scientist, author, statesman
De Augmentis Scientiarum [Advancement of Learning], Book 1, ch. 5, sec. 8 (1605)
Alt trans. (Willey Book ed., (1944)): "If we begin with certainties, we shall end in doubts; but if we begin with doubts, and are patient with them, we shall end in certainties."
How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?
Arthur Conan Doyle (1859-1930) British writer and physician
Story (1890-02), “The Sign of the Four,” ch. 6 [Holmes], Lippincott’s Monthly Magazine, Vol. 45 (US) / 1 (UK)
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The first appearance of the phrase in its most quoted form. However, earlier in the story, chapter 1, Holmes tells Watson:Eliminate all other factors, and the one which remains must be the truth.
Similar expressions occur in The Adventures of Sherlock Holmes ("The Adventure of the Beryl Coronet"), The Memoirs of Sherlock Holmes ("Silver Blaze"), The Return of Sherlock Holmes ("The Adventure of the Priory School"), His Last Bow ("The Adventure of the Bruce-Partington Plans"), and The Case-Book of Sherlock Holmes ("The Adventure of the Blanched Soldier").
The original publication, and Doyle's manuscript (along with many other iterations across media) use "The Sign of the Four" as the title, while others (including the first book publications) use "The Sign of Four." The five-word form is used most commonly in the story, but the four-word form does show up. (More info.)
Published in novel form as The Sign of Four (1890-10).