As we all know, Sherlock Holmes uses deduction to solve his mysteries. A friend said Sherlock didn’t use deduction, but induction. Was Sherlock Holmes wrong or did my friend made a mistake in reasoning?

Induction and deduction are both methods of reasoning. But what do they mean, and which is what? To find out we must define induction and deduction.

Afterwards we can draw a conclusion.

Given that we’re questioning things anyway, Sherlock Holmes apparently never said “Elementary, my dear Watson”

What is induction?

Induction is a way of proving things by showing that nothing else is possible then the options given.

You start by defining the statement and then you supply evidence. You exclude all other options. For example:

  • Statement: All the Swans are white.
  • 1: All the Swans in the Netherlands are white.
  • 2: All the Swans in Germany are white.
  • Exclusion: I have not seen any other Swans.
  • Therefor all the Swans are white.

The problem how ever, even though there are no black swans in Europe, there are in Australia. The above was true for many years, until Europeans reached Australia.

What is deduction?

Logical deduction is the opposite. With the deduction you are given a set of facts and from these facts you draw a conclusion.

  • Fact 1: It rains outside.
  • Fact 2: When it rains everything thats outside is wet.
  • Fact 3: I am outside.
  • Conclusion: I get wet.


I wrote this article because a friend of mine made the statement that Sherlock Holmes uses induction instead of deduction.

With induction you prove what your statements. With deduction you have facts and use those facts to draw a conclusion.

Sherlock, to my opinion, found facts and then drew conclusions.

Therefor, by using induction we’ve proven that sherlock uses deduction.

Case closed.