Elementary

In continuing with my explanation of logical reasoning as they can apply to detective work I'll be reviewing the differences in deduction, abduction, and induction.

Last post I stated that Sherlock incorrectly refers to his brand of logical reasoning as deduction, when it is, in fact, abductive reasoning. What's the difference? Well, deduction (in boring formula form) is deriving b from a, where b is a formal consequence of a. For example, if only female lions can get pregnant and a lion is pregnant, then that lion must be female. Given the truth of the assumption, the deduction is consequently true. Abduction is slightly different in that the truth of the  assumption is not guaranteed, and  therefore our abduction is also not guaranteed. For example, if you happen to see someone laying at the bottom of a flight of stairs, you could assume they tripped and fell, when  in fact they could have been pushed, or perhaps they simply enjoy napping at the bottom of the stairs. The person falling down the stairs is the hypothesis that explains our observation, but only one of many. Induction is also different in that our observations may give us good cause to believe something, though our conclusion may not be true. For example, a person might assume all fish swim underwater because all the fish they've seen thus far swim underwater. This same person would then be quite startled to see fish walking on land and gliding over the ocean.

That concludes my explanation of the three forms of logical reasoning. Next post I'll dive into a different, as yet to be determined, topic.

The Blog, Mr. Watson, is Afoot!

This is my first blog posting, and outside of pop culture references the only experience I have with the concept is The Professional Blog of Doctor John Watson from the excellent BBC Series Sherlock, which is a modern re-imagining of Sir Arthur Conan Doyle's hero. As a fan of detective stories I was quite taken with the show and Sherlock's intuitive deductions, and as this blog will be relating to the criminal justice field, what better topic to start with?

Sherlock Holmes's method of deduction is based on simple observation and reasoning and is actually a technique called "abductive reasoning”, and not deduction at all. In the short story A Scandal in Bohemia Sherlock was able to deduce that Watson had been in inclement weather and had a clumsy serving girl based solely off a glance at his shoes. When asked how he could know this Sherlock replied, “It is simplicity itself ... My eyes tell me that on the inside of your left shoe, just where the firelight strikes it, the leather is scored by six almost parallel cuts. Obviously they have been caused by someone who has very carelessly scraped round the edges of the sole in order to remove crusted mud from it. Hence, you see, my double deduction that you had been out in vile weather, and that you had a particularly malignant boot-slitting specimen of the London slavey.” As you can see, based on the powers of observation and logical reasoning Sherlock was able to display his prowess in deduction.

Next post I'll go into more detail about the differences between Deduction, Abduction, and Induction. Until then, may you observe, rather than simply see.