Sherlock Holmes: Lessons on Critical Thinking and Problem-Solving

sherlock holmes

While a fictional character, Sherlock Holmes is an excellent example of critical thinking and problem-solving that we can all learn from. Here’s a breakdown of his philosophy and approach to thinking.

As many of you know, I’ve been reading fiction a lot more this year, so I’ve been going through a lot of classics I’ve never had the chance to before.

Recently I finished reading A Study in Scarlet by Arthur Conan Doyle (1887). It’s the first novel to feature the legendary detective Sherlock Holmes. The book is a short, fun, and clever read – which I recommend to anyone – and Holmes is a great example of rationality and critical thinking.

As a private detective and consultant, Holmes sets himself apart from other detectives in the book through his unique ability to observe and analyze a situation and draw conclusions that seem to elude the average mind. This is why folks in the book are constantly visiting him and asking him for his input and advice.

Sherlock Holmes knows how to see things others don’t through his keen sense of observation, he knows what facts to focus on and which to ignore, and he knows how to deduce those facts to their logical, inevitable conclusions.

While of course Sherlock Holmes is a fictional character, he can still serve as a great role model when it comes to critical thinking and problem-solving.

Here are the big highlights and takeaways when it comes to his thinking philosophy.

Don’t fill your “brain attic” with useless knowledge

Sherlock Holmes sees his brain as an “empty attic” that can only be filled with so many facts and knowledge. Thus, he makes it an important point to never fill it with useless junk.

    “I consider that a man’s brain originally is like a little empty attic, and you have to stock it with such furniture as you choose. A fool takes in all the 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 with a lot of other things, so that he has a difficulty in laying his hands upon it. Now the skillful 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 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 forget something that you knew before. It is of highest importance, therefore, not to have useless facts elbowing the useful ones.”

Dr. Watson, who narrates the book and begins as a roommate of Sherlock Holmes, is always intrigued by Holmes odd ways and philosophies.

When trying to figure out what makes Sherlock tick, Watson discovers that he has excellent knowledge in certain areas in life (such as chemistry, botany, anatomy, and geology), but is also terribly ignorant on other matters (such as politics, contemporary literature, and astronomy).

In fact, when pressed, Sherlock Holmes admits he didn’t know that the earth revolved around the sun. Dr. Watson is shocked by this basic ignorance, but Holmes responds…

    “What the deuce is it to me? You say we go round the sun. If we went round the moon it would not make a pennyworth of difference to me or my work.”

This type of ruthless pragmatism is very characteristic of Sherlock Holmes philosophy. He doesn’t bother with a fact unless it has a direct impact on himself and his work.

To Holmes, a trivial or useless fact is just as good as a lie or a distraction from what really matters – something that only serves to crowd his brain attic.

The science of observation and deduction

Sherlock Holmes is best known for his power of deduction. Deduction is when you begin with a set of facts and then work your way backwards to their logical conclusion.

Throughout the book, Holmes makes many remarkable conclusions by observing simple facts and then reasoning backwards. One early example in the book describes how Holmes recognized Dr. Watson had just come back from Afghanistan.

    “From long habit the train of thought 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.”

By noticing physical features such as how the man walks, his mannerisms, his tanned skin, the features of his face, and how he moves his arms, Holmes was able to reason that this man was an English army doctor who had just come back from a hot region, therefore he must be coming back from Afghanistan (the British were fighting in Afghanistan at the time in the late 19th century).

Holmes makes many similar observations throughout the book, such as being able to estimate a person’s height based on his walking gait (as revealed by footprints in the ground), and noticing a cab must have stopped at the location of a crime (because the tire tracks are thinner than normal cabs).

A big part of Holmes’ genius is the ability to observe a tiny fact and recognize all the other facts that must logically be associated with it.

He goes on to tell Dr. Watson how his reasoning abilities are different than most people…

    “Most people, if you describe a train of events to them, will tell you what the result would be. They can put those events together in their minds, and argue from them that something will come to pass. There are 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 backwards.”

While most people observe “causes” and infer the “results” that will follow, Holmes prides himself in being able to start with the “results” and reason his way backwards to their original “causes.”

The value of strange facts

The stranger a fact is, the more revealing it can be.

According to Sherlock Holmes’ philosophy, ordinary facts aren’t very helpful because they can fit into a wide-range of scenarios. But a strange fact – a fact that stands out – can help you to narrow your options and point you in the right direction.

If a person is wearing a blue shirt, that doesn’t tell you much about them because a lot of people wear blue shirts. It’s too common to tell you anything important. But if a person is wearing a multi-colored armor vest, that raises all types of questions that could potentially lead you to an interesting truth.

Typically, the more bizarre a situation is, the more difficult you would think it is to explain. But for Holmes, using his power of deduction, he can take a mysterious fact and see how it illuminates the truth rather than hides it.

After solving a case, he explains to Watson…

    “All this seems strange to you, because you failed at the beginning of the inquiry to grasp the importance of the single real clue which was presented to you. I had the good fortune to seize upon that, and everything has occurred since then has served to confirm my original supposition, and indeed, was the logical consequence of it. Hence things which have perplexed you and made the case more obscure have served to enlighten me and to strengthen my conclusions. It is a mistake to confound strangeness with mystery, because it presents no new or special features from which deductions may be drawn. This murder would have been infinitely more difficult to unravel had the body of the victim been simply found lying in the roadway without anyone of those outré and sensational accompaniments which have rendered it remarkable. These strange details, far from making the case more difficult, have really had the effect of making it less so.”

If you know a strange truth, then you have to factor it into your understanding – that’s going to lead you down certain pathways, while blocking other ones.

This reminds me of a great quote by Isaac Asimov, “The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka’ but ‘That’s funny…’”

As a scientist, detective, or truth-seeker, strangeness often points you in a direction you need to pursue further.

The need for deep contemplation

While Sherlock Holmes is generally depicted as energized and pro-active throughout the book, it’s also noted how he has intense periods of contemplation.

Early on, his roommate Dr. Watson makes an alarming observation when Holmes gets into his solitary moods…

    “Nothing could exceed his energy when the working fit was upon him; but now an again a reaction would seize him, and for days he would lie upon the sofa in the sitting-room, hardly uttering a word or moving a muscle from morning to night. On these occasions I have notice such a dreamy, vacant expression in his eyes, that I might have suspected him of being addicted to the use of some narcotic, had not the temperance and cleanliness of his whole life forbidden such a notion.”

There’s not much else said about these behaviors, so we have to speculate a bit. Since Holmes had a consistent schedule when it came to sleep, diet, and work, it’s safe to say these odd behaviors aren’t due to over-exertion or working too hard.

Most great minds need moments of healthy reflection to process all the information they’ve absorbed throughout the day. A hyper-active and hyper-observant mind such as Sherlock’s probably needs more time to digest and think than others.

The “dreamy, vacant expression” seems to refer to a person looking inward, tuning out the outside world, and thinking deeply.

There are other eccentricities to Sherlock Holmes that relate to his thinking and problem-solving abilities. The biggest one is probably his habit of playing the violin.

    “[His powers of the violin] were very remarkable, but as eccentric as all his other accomplishments. There he could play pieces, and difficult pieces, I knew well, because at my request he has played me some of Mendelssohn’s Lieder, and other favorites. When left to himself, however, he would seldom produce any music or attempt any recognized air. Leaning back in his arm-chair of an evening, he would close his eyes and scrape carelessly at the fiddle thrown across his knee. Sometimes the chords were sonorous and melancholy. Occasionally they were fantastic and cheerful. Clearly they reflected the thoughts which possessed him, but whether the music aided those thoughts, or whether the playing was simply the result of a whim or fancy, was more than I could determine.”

When left to his own devices and not playing a popular piece of classical music for Watson, Holmes seems to use the violin as an improvisational tool to get more in touch with his inner thoughts and feelings.

As a musician myself who likes to improvise, I often see music as a way to “think without words” – it’s another way for me to reflect on and digest my experiences that doesn’t require language or conversation.

It’s possible Sherlock uses the violin as a way to take a break from his busy mind (a form of leisure or self-care), or that he uses it as an extension of his mind to help think more clearly and get in touch with his gut and intuition.

Whatever the case may be, Sherlock’s violin playing is an important part of his daily routine and what makes him who he is.


Sherlock Holmes is a great example of an intelligent and inquisitive mind. A Study in Scarlet is a fun introduction to his strange ways and what makes him tick. I’m looking forward to reading more stories about him in the future to dive deeper into what makes him such a unique and memorable character.

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