“There is nothing more deceptive than an obvious fact.” – Sherlock Holmes

From Netflix´s Enola Holmes, BBC´s Sherlock with Benedict Cumberpatch, to the third instalment of the Sherlock Holmes movies with Robert Downey Jr and Jude Law, Sherlock Holmes remains one of the most beloved fictional characters of pop culture.

I was always fascinated by the seemingly unsolvable complex crimes Sherlock Holmes easily untangled by the end of every story. Reading the paper “The abduction of Sherlock Holmes” by David Carson, I learned about the theory behind this process and how it could apply to all of our lives.

The paper connects these insights to the training of police officers and I recommend anyone interested in reading the whole thing: Carson, D. (2009). The Abduction of Sherlock Holmes. International Journal of Police Science & Management, 11(2), 193–202. https://doi.org/10.1350/ijps.2009.11.2.123

Below are some of the key points partially directly quoted to explain what I got out of it.

To start, it is all about inferential reasoning. This is the process of supposing further knowledge from that which we already possess (or believe we possess). For example, there are dark clouds in the sky, so it will probably rain soon.

This inferential reasoning can happen in three forms: Deduction, induction, and abduction.

Deduction is discovering the implications of what we already know. Most famous for this are syllogisms used in logic. For instance:

All men are mortal. Socrates is a man. Therefore, Socrates is mortal.

It is important to note that deduction tells you not more than what is already known.

Induction is common in physical science. You create more knowledge but not necessarily correct conclusion. It is about observing a phenomenon, drawing conclusions, and then generalising from then. This might not always be 100% correct and only scientific rigour and a trustworthy methodology can make it better. Induction also tends to have a positivistic perspective. It accepts that facts exist independent of observation and that observers can see, hear or otherwise sense data without affecting them.

This is contrary to abduction. Here facts cannot be understood independent of how we observe and understand them. Abduction is the process of forming an explanatory hypothesis. When we perceive something, we interpret it, we make sense of something. It is the only logical operation out of these three which introduces any new idea.

All of these combined can be see as three stages in an inquiry. First, the abduction creates the hypothesis, then induction tests that theory, lastly, deduction allows you to work out the necessary consequences.

Often abduction is not used enough because once you have a hypothesis, you often stick with it or try to fit in new facts within it. This is the risk of the confirmation bias.

The confirmation bias is the tendency to listen more often to information that confirms our existing beliefs. Through this bias, people tend to favour information that reinforces the things they already think or believe.

All in all, being aware of these forms of inferential reasoning helps us being more clear in our own thinking. If I encounter a complex problem, I first take the perspective of Sherlock Holmes and try to figure out what happened based on the facts. Then, I would test these theories with a scientific methodology while being open to new hypotheses to avoid a confirmation bias. Lastly, I try to base my decision in deduction of how I usually would act or believe in to be ethically correct.

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