The Science of Deduction and Analysis.

Ever read about Science of observation, deduction and analysis? Oh, I’m not going to give a physics lecture if that's what you're thinking ! Well, it’s a grate thing. Imagine that somebody is coming to you and you already know what s/he was up to in the past or what s/he is going to ask you and so on… there could be many cases in which science of deduction can be used. Here are some of the points which can help you all in deducing. I found them to be highly interesting and useful. 

But you can always read novels of Arthur Conan Doyle in your leisurely time to known more about it. They are available on the net as e-books for free, and in printed form as well. 

SHERLOCK HOLMES’ SCIENCE OF DEDUCTION AND ANALYSIS 
Note: Nos. 1-60 are from the Doyle complete canon; 61-94 are from the Basil Rathbone movies, and 95-97 are from the Young Sherlock Holmes movie.

1. 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 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 inquirer in any case is almost inconceivable.
2. 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.
3. 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.
4. 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.
5. It is a capital mistake to theorize before you have all the evidence. Insensibly, one begins to twist the facts to suit theories, instead of theories to suit facts. It biases the judgment.
6. The temptation to form premature theories upon insufficient data is the bane of this profession.
7. They say that genius is an infinite capacity for taking pains. It’s a very bad definition, but it does apply to detective work.
8. The height of a man, in nine cases out of ten, can be told from the length of his stride.
9. When a man writes on a wall, his instinct leads him to write above the level of his own eyes.
10. To a great mind, nothing is little.
11. 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.
12. There is nothing new under the sun. It has all been done before.
13. 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.
14. 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.
15. Detection is, or ought to be, an exact science and should be treated in the same cold and unemotional manner.
16. Never guess. It is a shocking habit – destructive to the logical faculty. Observe the small facts upon which large inferences may depend.
17. When you have eliminated the impossible, whatever remains, however improbable, must be the truth.
18. 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.
19. Women are never to be entirely trusted – not the best of them.
20. 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.
21. When someone thinks their house is on fire, their first instinct is at once to rush to the thing which they value most. It is a perfectly overpowering impulse.
22. 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.
23. 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.
24. 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.
25. It should be your business to know things. To train yourself to see what others overlook.
26. In an investigation, the little things are infinitely the most important.
27. 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.
28. Singularity is almost invariably a clue. The more featureless and commonplace a crime is, the more difficult it is to bring it home.
29. The most difficult crime to track is the one which is purposeless.
30. Depend on it, there is nothing so unnatural as the commonplace.
31. You must look for consistency. Where there is a want of it you must suspect deception.
32. 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.
33. 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.
34. Your method should be founded upon the observation of trifles.
35. 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.
36. Often the impression of a woman may be more valuable than the conclusion of an analytical reasoner.
37. Read nothing but the criminal news and the agony column. The latter is always instructive.
38. 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.
39. 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.
40. Crime is common. Logic is rare. Therefore it is upon logic rather than upon crime that you should dwell.
41. Pipes are occasionally of extraordinary interest. Nothing has more individuality, save perhaps watches and bootlaces.
42. 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.
43. 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.
44. 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.
45. Make it a point of never having any prejudices, and of following docilely wherever a fact may lead you.
46. In an investigation, it is only the colourless, uneventful cases which are hopeless.
47. In an investigation, always look for a possible alternative, and provide against it. It is the first rule of criminal investigations.
48. 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.
49. Some people without possessing genius have a remarkable power of stimulating it.
50. 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.
51. The Press is a most valuable institution, if you only know how to use it.
52. 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.
53. Education never ends. It is a series of lessons with the greatest for the last.
54. First real insight into the character of parents is gained by studying their children.
55. 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.
56. When a doctor does go wrong he is the first of criminals. He has the nerve and he has the knowledge.
57. When you follow two separate chains of thought, you will find some point of intersection which should approximate to the truth.
58. 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.
59. It is always good to have someone with you on whom you can thoroughly rely. Local aid is always either worthless or else biased.
60. 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.
61. The average petty thief has a more extensive knowledge of the value of objects, than the average collector.
62. The best place to hide anything, is where everyone can see it.
63. It’s often a mistake to accept something as true, merely because it’s obvious. The truth is only arrived at by the painstaking process of eliminating the untrue.
64. One of the first principles in solving crime, is never to disregard anything, no matter how trivial.
65. People generally forget in assuming a disguise, that the shape of the ear is an almost infallible means of recognition and identification to the trained eye.
66. Facts are always convincing. It’s the conclusions drawn from facts, that are frequently in error.
67. To the trained ear, footsteps have a characteristic rhythm as identifiable as fingerprints.
68. When murders are committed, there usually is something that unfortunate victims have in common, that might indicate the motive. If, on the other hand, they appear incidental, then they are sometimes a part of something more sinister.
69. The science of detection is very much like stringing a handful of beads. In an investigation, the suspects are the beads, where you then must try to string them together with some thread to make a connection, in order to solve the mystery.
70. Houses, like people, have definite personalities.
71. Surgical instruments that save life, are hardly more pleasant to look at, than those that take it.
72. Murder like matrimony, generally has a motive.
73. In this profession, one has to take chances.
74. Egomaniacs are always so much more chatty when they feel they have the upper hand.
75. Suicides, invariably leave notes behind them. Murders do not, and when you drive a person to suicide, that’s murder.
76. Often a good disguise to assume, is that of a postman. No one ever looks twice at a postman.
77. When women are involved in crime, their method, whatever it is, is apt to be peculiarly subtle and cruel. Feline not canine.
78. Poison is a woman’s weapon.
79. Whenever setting a trap, in order to catch someone, it’s best to bait it with the food they like.
80. In an attempt to solve a crime, it’s best to duplicate the conditions under which the crime occurred.
81. Never trust plans already made by other people, they have a habit of becoming to widely known.
82. Sometimes to leave one unguarded, can be a skillful trap for one’s opponent.
83. The imagination is where crimes conceived, and where they’re solved.
84. Even when facts clearly indicate one thing, it is not always the case. That’s why so many murders remain unsolved. People will stick to facts, even though they prove nothing. Now, if you go beyond facts, use the imagination as the criminal does, imagine what might have happened, and act upon it, you will usually find yourself justified.
85. An investigator always needs something more than legends and rumors. Proof, you must have proof.
86. When examining footprints, it’s good to know that, clubfooted people invariably bring their full weight down on the toe. If other peculiarities arise, such as, the footprint being balanced from toe to heel, then the footprint must have some other compensating deformity to explain it, such as, the footprint being made by a person not really clubfooted, but wearing a clubfooted shoe.
87. The obvious always appears simple.
88. No matter what situation arises, one must adapt oneself to the tools at hand.
89. Every crime, always exhibits a pattern and a purpose in it.
90. Purpose and motive are the last things a sane man would imply, if he were posing as a madman. Unless there is method in his madness.
91. The temptation of the sudden wealth, could possibly turn a once seemingly harmless person, into a ruthless killer.
92. Murder is an insidious thing. Once a person has dipped their fingers in blood, sooner or later they’ll feel the urge to kill again.
93. The terrifying part about blackmail is, that the victim is afraid to fight the accusation, no matter how false. Once the accusation is made, their name becomes smeared and sometimes their life is ruined.
94. Anything is possible, until proven otherwise.
95. Never trust the obvious.
96. The deductive mind never rests. It’s not unlike a finely tuned musical instrument, which demands attention and practice. Problems of logic, mathematical equations and riddles are some ways of fine-tuning the mind.
97. A great detective relies on perception, intelligence, and imagination.

“Come, Watson, come! The game is afoot.”