Lessons from the Master of Deduction

May 13 2013

“Tell me to what you pay attention, and I will tell you who you are.” - W.H. Auden

In Mastermind, Maria Konnikova uses the stories of Sherlock Holmes to lay out best practices for deduction, observation, memory and imagination for anyone who wants to be a consulting detective (including market researchers). Some of the key lessons are worth repeating and a good addition to a previous article on Sherlock Holmes, summarised as:

  1. Know yourself
  2. Observe carefully
  3. Imagine
  4. Deduce
  5. Learn

Know yourself and your environment

Awareness (or ‘mindfulness‚Äô) of the world around you is an important part of Sherlock Holmes‚Äô method. In the words of William James (the founder of modern psychology), “the faculty of voluntarily bringing back a wandering attention, over and over again, is the very root of judgment, character and will”. Sherlock Holmes demonstrates again and again the importance of focused attention, sometimes to the extremes of ignoring those around him and the basics of life. The skill of focusing on a task (or being ‘in the flow‚Äô) is increasingly difficult in today‚Äôs world of short attention spans and constant demands from email, social media and demanding business environments.

Multiple research studies have demonstrated the value of meditation for periods as short as fifteen minutes each day - leading to feeling younger, improving blood pressure and, of course, better cognitive function. Looking at scenes of nature can also improve insight, creativity and productivity. Despite the claims of many, we are very poor at multitasking (which should be renamed task switching as it really consists of constantly shifting focus between tasks, leading to poorer performance on all of them).

Observe carefully and thoughtfully

The best observation is directed and mindful, combining seeing with an active, rather than passive, attention to those details which are important in the context of your observation. This means that you need to be selective about what you pay attention to - remembering that the brain is filtering a vast amount of sensory data, ensuring that 11 million pieces of information each second, are manageable to our conscious (System 2) brains that can manage no more than 40.

You should also be objective in the way you observe (avoiding the confirmation bias that researchers are prone to), inclusive in the way you seek data and engaged in your subject, your participants and your environment.  Observation is contingent on the environment and context too, through considering the story (or stories) that might lie behind the immediately observable data.


Although Sherlock Holmes makes far more use of System 2 (the rational brain) than most of us, but he also has a great imaginative capability and is often highly creative in the way he uncovers the truth. This is based on his ability to imagine different possibilities, even those which may prove wrong. He even occasionally fails, proving that you have to fail sometimes in order to be successful most of the time.

Holmes works hard to avoid some of our common mental biases, such as availability bias, by deliberately thinking through alternatives that others might ignore as unlikely. Famously he states, “when you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth”. His imagination is helped by his focus on using his ‘memory attic‚Äô to store all kinds of information which may eventually be helpful in solving a crime. Holmes makes a deliberate policy of ensuring that he remembers the right information and ignores information that is not relevant to his job - most famously in one story he claims to not remember the latest scientific theories of planetary orbits as they are not important to him.


In one story, Holmes calls deduction “systematised common sense”, although in formal logic, it‚Äôs arguable that everything Holmes does is deduction as he also uses induction and most frequently abduction. Abduction is a form of logical inference that moves from the description of data to hypotheses that account for the evidence (which Charles Sanders Peirce, who invented the term, called ‘guessing‚Äô). Arguably, Holmes makes many ‘educated guesses‚Äô (in more polite language), as he draws conclusions based on the best possible explanation of the facts (see above, “when you have … “).

Abduction relies on economy of explanation (Occam‚Äôs razor), and the conclusions of abductive reasoning are never guaranteed, as demonstrated in many Holmes stories, when his initial conclusions are proved wrong, although they were the best possible explanation of the available evidence, until new evidence comes to light. Often this new evidence comes to light, because of the questions raised by Holmes abductive ‘leaps of imagination‚Äô.

Learn from your mistakes

Holmes famously does learn from the mistakes he makes, although he makes far fewer than those around him. He uses mistakes to re-evaluate data and learn something new, deconstructing and then reconstructing his previous theories. And famously, but only very occasionally, he will ask Watson to remind him of his own shortcomings.

We can all learn from Sherlock Holmes‚Äô methods. Although his skills of ‘deduction‚Äô are unsurpassed there are many lessons for all of us in the way he approaches his work, including the quest for constant learning. Mastermind is an interesting read for any fans of Sherlock Holmes and anyone interested in improving their investigative skills.


Complete Sherlock Holmes by Sir Arthur Conan Doyle

Mastermind: How To Think Like Sherlock Holmes by Maria Konnikova

One response so far

  1. Professor Moriarty

    Holmes is not as good as me.
    I am the master. Find my mathematical theories on the next blog.

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