Current Affairs Journal: Eighth Entry

My last post about criminal profiling made me think about something sci-fi-related. If any of you have ever seen an episode of Sherlock (or maybe even the movies, which I actually haven’t seen) you have seen that he has his trademark habit of deducing facts from looking at people, places, situations or whatnot. So I started wondering if Sherlock himself maybe uses offender profiling of some sort to make his deductions. This post here presents the result of my research on what tools Sherlock uses to draw his deductions.

The first thing I came across is this huge debate whether Sherlock uses deductive or inductive reasoning for his deductions? As it seems Arthur Conan Doyle himself described Sherlock as someone who uses deductive reasoning (seems logical if it’s “deductions” that Sherlock draws). It is suggested from more sources than one, though, that even in the books Sherlock used inductive reasoning or both deductive and inductive reasoning.

Now, first things first: What is inductive/deductive reasoning?

Deductive reasoning (top-down logic) consists of four logical steps that need to be taken to come to a conclusion: Theory-hypothesis-observation-confirmation. You start with a theory about something you are interested in. Then you find a hypothesis for this theory which can be tested using different observations. This way, you can see if your theory is right. An easy example for this would be the following thing I found on the internet.

“Since all humans are mortal, and I am a human, then I am mortal.”
“All numbers ending in 0 or 5 are divisible by 5. The number 35 ends with a 5, so it is divisible by 5.”
(Hypothesis – Observation – Confirmation)

What deductive reasoning is all about therefore, is coming from a broader theory to a specific conclusion and to find out whether it is true or not. In other words: “drawing logical conclusions” or “from general to specific”. It is important to mention, though, that these logical conclusions are only valid if the initial theory and the argument itself is correct. If it isn’t, the result can’t be correct either.

Inductive reasoning is the opposite of deductive reasoning. It is also called “Bottum-up logic” and works like this: You move from “specific observations” to “broader generalizations”. Your conclusion depends entirely on your interpretation, though, which means an inductive argument can  be wrong. Your inductive argument is actually just a good guess. An example for inductive reasoning would be the following:

• Every tornado I have ever seen in the United States rotated counterclockwise, and I have seen dozens of them. (specific observation)
• We see a tornado in the distance, and we are in the United States.
• I conclude that the tornado we see right now must be rotating counter clockwise.(broader generalisation)

Now we know that what Sherlock Holmes does in the books, films or movies is reasoning backwards. If we look at certain clips of Sherlock Holmes movies or scenes from the TV show you can see and have a look yourself. What do you think it is that he does? Inductive or deductive reasoning?? I personally believe it is inductive reasoning but I might be wrong. This topic still makes my head spin ‘cause it is reaaally really confusing. But just try and take a guess yourself!

Sherlock deducing John Watson

Now last but not least, is inductive/deductive reasoning just something that occurs in science fiction or is it also used by forensic scientists? Now this is where this text connects with the beginning of the post: inductive/deductive reasoning is used in criminal profiling (not exclusively in offender profiling, though!). Arthur Conan Doyle’s stories about Sherlock Holmes are actually even used to teach inductive/deductive reasoning for different criminal justice professions.^^ 

Well after such a long post everything that is left to say is the following: Fact 1, Fiction 0.