Mastermind: How to Think Like Sherlock Holmes (24 page)

Holmes gets to the very heart of the matter in
The Valley of Fear
, when he admonishes Watson that “there should be no combination of events for which the wit of man cannot conceive an explanation. Simply as a mental exercise, without any assertion that it is true, let me indicate a possible line of thought. It is, I admit, mere imagination; but how often is imagination the mother of truth?”

SHERLOCK HOLMES FURTHER READING

“Here is a young man who learns suddenly . . .” “Not until I have been to Blackheath.”
from
The Casebook of Sherlock Holmes
, “The Adventure of the Norwood Builder,” p. 829.

“You will rise high in your profession.”
from
His Last Bow
, “The Adventure of Wisteria Lodge,” p. 1231.

“One of the most remarkable characteristics of Sherlock Holmes was his power of throwing his brain out of action . . .”
from
His Last Bow
, “The Adventure of the Bruce-Partington Plans,” p. 297.

“It is quite a three-pipe problem . . .”
from
The Adventures of Sherlock Holmes
, “The Red-Headed League,” p. 50.

“I have been to Devonshire.”
from
The Hound of the Baskervilles
, chapter 3: The Problem, p. 22.

“I’m a believer in the
genius loci.”
“Breadth of view, my dear Mr. Mac, is one of the essentials of our profession.”
from chapter 6: A Dawning Light, p. 51; chapter 7: The Solution, p. 62
The Valley of Fear.

PART THREE

CHAPTER FIVE

Navigating the Brain Attic: Deduction from the Facts

I
magine you are Holmes, and I, Maria, a potential client. You’ve spent the last hundred-odd pages being presented with information, much as you would if you were to observe me in your sitting room for some time. Take a minute to think, to consider what you may know about me as a person. What can you infer based on what I’ve written?

I won’t go down the list of all possible answers, but here’s one to make you pause: the first time I ever heard the name Sherlock Holmes was in Russian. Those stories my dad read by the fire? Russian translations, not English originals. You see, we had only recently come to the United States, and when he read to us, it was in the language that my family uses to this day with one another at home. Alexandre Dumas, Sir H. Rider Haggard, Jerome K. Jerome, Sir Arthur Conan Doyle: all men whose voices I first heard in Russian.

What does this have to do with anything? Simply this: Holmes would have known without my having to tell him. He would have made a simple deduction based on the available facts, infused with just a bit of that imaginative quality we spoke about in the last chapter. And he would have realized that I couldn’t have possibly had my first encounter with his methods in any language but Russian. Don’t believe me? All of the elements are there, I promise. And by the end of this chapter, you, too, should be in a position to follow Holmes in putting them together into the only explanation that would suit all of the available facts. As the detective says over and over, when all avenues are exhausted, whatever remains, however improbable, must be the truth.

And so we turn finally to that most flashy of steps: deduction. The grand finale. The fireworks at the end of a hard day’s work. The moment when you can finally complete your thought process and come to your conclusion, make your decision, do whatever it was that you had set out to do. Everything has been gathered and analyzed. All that remains is to see what it all means and what that meaning implies for you, to draw the implications out to their logical conclusion.

It’s the moment when Sherlock Holmes utters that immortal line in “The Crooked Man,”
elementary.

“I have the advantage of knowing your habits, my dear Watson,” said he. “When your round is a short one you walk, and when it is a long one you use a hansom. As I perceive that your boots, although used, are by no means dirty, I cannot doubt that you are at present busy enough to justify the hansom.”

“Excellent!” I cried.

“Elementary,” said he. “It is one of those instances where the reasoner can produce an effect which seems remarkable to his neighbour, because the latter has missed the one little point which is the basis of the deduction.”

What does deduction actually entail? Deduction is that final navigation of your brain attic, the moment when you put together all of the elements that came before in a single, cohesive whole that makes sense of the full picture, the attic yielding in orderly fashion what it has gathered so methodically. What Holmes means by deduction and what formal logic means by deduction are not one and the same. In the purely logical sense, deduction is the arrival at a specific instance from a general principle. Perhaps the most famous example:

All men are mortal.

Socrates is a man.

Socrates is mortal.

But for Holmes, this is but one possible way to reach the conclusion. His deduction includes multiple ways of reasoning—as long as you proceed
from fact and reach a statement that must necessarily be true, to the exclusion of other alternatives.
³

Whether it’s solving a crime, making a decision, or coming to some personal determination, the process remains essentially the same. You take all of your observations—those attic contents that you’ve decided to store and integrate into your existing attic structure and that you’ve already mulled over and reconfigured in your imagination—you put them in order, starting from the beginning and leaving nothing out, and you see what possible answer remains that will both incorporate all of them and answer your initial question. Or, to put it in Holmesian terms, you lay out your chain of reasoning and test possibilities until whatever remains (improbability aside) is the truth: “That process starts upon the supposition that when you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth,” he tells us. “It may well be that several explanations remain, in which case one tries test after test until one or other of them has a convincing amount of support.”

That, in essence, is deduction, or what Holmes calls “systematized common sense.” But the common sense is not as common, or as straightforward, as one might hope. Whenever Watson himself tries to emulate Holmes, he often finds himself in error. And it’s only natural. Even if we’ve been accurate up to this point, we have to push back one more time lest System Watson leads us astray at the eleventh hour.

Why is deduction far more difficult than it appears? Why is it that Watson so often falters when he tries to follow in his companion’s footsteps. What gets in the way of our final reasoning? Why is it so often so difficult to think clearly, even when we have everything we need to do so? And how can we circumvent those difficulties so that, unlike Watson, who is stuck to repeat his mistakes over and over, we can use System Holmes to help us out of the quagmire and deduce properly?

The Difficulty of Proper Deduction:
Our Inner Storyteller at the Wheel

A trio of notorious robbers sets its sights on Abbey Grange, the residence of Sir Eustace Brackenstall, one of the richest men in Kent. One night, when all are presumed to be sleeping, the three men make their way through the dining room window, preparing to ransack the wealthy residence much as they did a nearby estate a fortnight prior. Their plan, however, is foiled when Lady Brackenstall enters the room. Quickly, they hit her over the head and tie her to one of the dining room chairs. All would seem to be well, were it not for Sir Brackenstall, who comes in to investigate the strange noises. He is not so lucky as his wife: he is knocked over the head with a poker and he collapses, dead, onto the floor. The robbers hastily clear the sideboard of its silver but, too agitated by the murder to do much else, exit thereafter. But first they open a bottle of wine to calm their nerves.

Or so it would seem, according to the testimony of the only living witness, Lady Brackenstall. But in “The Adventure of the Abbey Grange,” few things are what they appear to be.

The story seems sound enough. The lady’s explanation is confirmed by her maid, Theresa, and all signs point to events unfolding much in the manner she has described. And yet, something doesn’t feel right to Sherlock Holmes. “Every instinct that I possess cries out against it,” he tells Watson. “It’s wrong—it’s all wrong—I’ll swear that it’s wrong.” He begins enumerating the possible flaws, and as he does so, details that seem entirely plausible, when taken one by one, now together begin to cast doubt on the likelihood of the story. It is not, however, until he comes to the wineglasses that Holmes knows for sure he is correct. “And now, on the top of this, comes the incident of the wineglasses,” he says to his companion.

“Can you see them in your mind’s eye?”

“I see them clearly.”

“We are told that three men drank from them. Does that strike you as likely?”

“Why not? There was wine in each glass.”

“Exactly, but there was beeswing only in one glass. You must have noticed that fact. What does that suggest to your mind?”

“That last glass filled would be most likely to contain beeswing.”

“Not at all. The bottle was full of it, and it is inconceivable that the first two glasses were clear and the third heaving charged with it. There are two possible explanations, and only two. One is that after the second glass was filled the bottle was violently agitated, and so the third glass received the beeswing. That does not appear probable. No, no, I am sure that I am right.”

“What, then, do you suppose?”

“That only two glasses were used, and that the dregs of both were poured into a third glass, so as to give the false impression that three people had been there.”

What does Watson know about the physics of wine? Not much, I venture to guess, but when Holmes asks him about the beeswing, he at once comes up with a ready answer: it must have been the last glass to be poured. The reason seems sensible enough, and yet comes from nowhere. I’d bet that Watson hadn’t even given it so much as a second thought until Holmes prompted him to do so. But when asked, he is only too happy to create an explanation that makes sense. Watson doesn’t even realize that he has done it, and were Holmes not to stop him for a moment, he would likely hold it as future fact, as further proof of the veracity of the original story rather than as a potential hole in the story’s fabric.

Absent Holmes, the Watson storytelling approach is the natural, instinctive one. And absent Holmes’s insistence, it is incredibly difficult to resist our desire to form narratives, to tell stories even if they may not be altogether correct, or correct at all. We like simplicity. We like concrete reasons. We like causes. We like things that make intuitive sense (even if that sense happens to be wrong).

On the flip side, we dislike any factor that stands in the way of that simplicity and causal concreteness. Uncertainty, chance, randomness, nonlinearity: these elements threaten our ability to explain, and to explain quickly and (seemingly) logically. And so, we do our best to eliminate them at every turn. Just like we decide that the last glass of wine to
be poured is also most likely to contain all the beeswing if we see glasses of uneven clarity, we may think, to take one example, that someone has a hot hand in basketball if we see a number of baskets in a row (the hot-hand fallacy). In both cases, we are using too few observations to reach our conclusions. In the case of the glasses, we rely only on that bottle and not on the behavior of other similar bottles under various circumstances. In the case of basketball, we rely only on the short streak (the law of small numbers) and not on the variability inherent in any player’s game, which includes long-run streaks. Or, to take another example, we think a coin is more likely to land on heads if it has fallen on tails for a number of times (the gambler’s fallacy), forgetting that short sequences don’t necessarily have to have the fifty-fifty distribution that would appear in the long term.

Whether we’re explaining why something has happened or concluding as to the likely cause of an event, our intuition often fails us because we prefer things to be much more controllable, predictable, and causally determined than they are in reality.

From these preferences stem the errors in thinking that we make without so much as a second thought. We tend to deduce as we shouldn’t, arguing, as Holmes would put it, ahead of the data—and often in spite of the data. When things just “make sense” it is incredibly difficult to see them any other way.

W.J. was a World War II veteran. He was gregarious, charming, and witty. He also happened to suffer from a form of epilepsy so incapacitating that, in 1960, he elected to have a drastic form of brain surgery. The connecting fabric between the left and right hemispheres of the brain that allows the two halves to communicate—his corpus collosum—would be severed. In the past, this form of treatment had been shown to have a dramatic effect on the incidence of seizures. Patients who had been unable to function could all of a sudden lead seizure-free lives. But did such a dramatic change to the brain’s natural connectivity come at a cost?