1. You see, but you do not observe

Sir Arthur Conan Doyle’s legendary detective Sherlock Holmes is, of course, a work of fiction. But is it actually possible to learn how to be a master of deduction?

Holmes solves the most bewildering of cases by thinking outside the box as well as inside – he even thinks about the box itself. It’s this attention to detail – all the details – that allows him to make the most extraordinary inferences.

How does he do it? Well it’s harder than you think, but it can be done. So get ready for a lesson in observation and reasoning as we welcome you to Sherlock’s school of thought.

2. The master at work

Mark Gatiss discusses Sherlock's power of deduction and shares an impressive observational anecdote of his own.

3. The science of deduction

"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.”

So says Holmes in the short story The Adventure of the Crooked Man. But, despite his own claims to the contrary, Sherlock’s powers of deduction are anything but elementary.

Making one connection might be easy enough but there’s a complex science to joining all the dots. Two sciences in fact, forensics and criminology, and Sherlock could be considered a pioneer of both.

Forensic science is the analysis of physical evidence to link a suspect to a crime. Holmes was quick to adopt some of the field’s innovative methods, using fingerprints to crack the case in Sign of Four, published in 1890. It was more than a decade before Scotland Yard adopted the practice in 1901.

The criminological field of offender profiling also has more than a shade of Sherlock to it. The investigative tool, which attempts to prevent and solve crimes by understanding what makes offenders tick, has been greatly influenced by that most Holmesian of concepts: deductive reasoning.

While things may have changed a little since Holmes’s heyday, the ability to make brilliant deductions is still underpinned by an extensive knowledge base: you can’t connect the dots if you don’t collect the dots.

Today’s law enforcers can also utilise a network of informers not too dissimilar to that of Sherlock. Criminal informants, CCTV and even programmes like Crimewatch can all help police find things they might otherwise have missed.

While Holmes had a remarkable range of skills for one man, contemporary investigation is conducted by a number of different specialists. But from blood and ballistics to psychologists and psychiatrists, Sherlock’s meticulous methods can still be evidenced in modern policing.

4. Mark meets the Deductionist

Mark Gatiss meets Colin Cloud, an entertainer who has been compared to Sherlock because of his Holmesian deduction skills.

5. A lesson in deduction

Fast emerging as a world leader in deduction, Colin Cloud explains the skills you need to think like Sherlock.

“‘You see, but you do not observe. The distinction is clear.’ These immortal words from A Scandal in Bohemia perfectly sum up the principal of deduction: don’t just look at what’s been presented to you, go beyond that and study the context too.

“Real deduction boils down to two things used in combination: your knowledge and sense of awareness. The more information you can gather, the more accurate your deductions are going to be.”

But how do you gather this information? What are the things that you can be picking up on?

“Pay attention. It's all there, laid bare before you. All you have to do is tune in to it. What do you see? Smell? Hear? Now think a little deeper. What direction is that siren in the distance travelling in? What’s that song coming through the headphones of the person next to you on the Tube?

“Look at someone, anyone. What can you infer? Do you notice marks, stains or foreign hairs on their clothes? What perfume are they wearing? Or do they smell of something else, like a particularly pungent foodstuff?

“If you embrace your senses your awareness will increase and, in time, you’ll know who people really are, what they feel and even what they’re thinking.”

6. Something to write Holmes about

Meet the real life characters who are said to be the inspiration behind Conan Doyle’s Sherlock.

Dr Joseph Bell

Image: Wellcome Library, London

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Dr Joseph Bell

1837-1911

Conan Doyle’s primary inspiration, Dr Bell was a surgeon and pioneer of forensic science whose diagnoses were based on keen observation and astute reasoning.

Henry Littlejohn

Image: Wellcome Library, London

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Henry Littlejohn

1826-1914

A police surgeon and medical adviser to the crown in Scotland, Littlejohn often worked alongside Bell to provide the forensic expertise to crack cases.

Jerome Caminada

Image: Greater Manchester Police Museum and Archives

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Jerome Caminada

1844-1914

The “terror to evil doers”, Manchester cop Caminada was a master of disguise, used a wide network of informers and even had his own Moriarty in Bob Horridge.