Forensic pathologist wants us to reconsider our homage to Holmes.
Posted May 30, 2018
Around the world, Sherlock Holmes is one of the most identifiable and highly regarded literary icons. No other fictional character has spun such a fan base nor been such a prominent role model for aspiring detectives. Throughout the history of forensic science, the greatest compliment has been to dub a skilled investigator as “the real-life Sherlock Holmes.”
However, forensic doctor and pathologist Thomas Young insists that we’ve been hoodwinked. The tricks of fiction have falsely portrayed an inferior method as a superior one. With plenty of experience and trial research behind him, he boldly states in his new book, The Sherlock Effect: How Forensic Doctors and Investigators Disastrously Reason Like the Great Detective, that using Holmes’ approach is a poor way to conduct forensic investigations. It has infected our legal system and caused many injustices.
Young begins with Holmes’ explanation to Watson of “reasoning backwards.” It works like this: Holmes learns about or observes a result – say, the death of a woman in her bedroom – and then uses intuition to describe the steps required for the incident to have occurred. “The reader is tricked into thinking that backwards reasoning is brilliant,” says Young, but it doesn’t actually work.
Here's why: “For any result, any set of clues, there may be numerous possible ‘trains of events’ that could explain the result.” Two plus two equals four, yes, but one cannot say that only by adding two and two can we get to four. So, any given “result” might have numerous possible routes, and one cannot be certain with intuition alone which one to pick.
This seems elementary, especially for complex cases, but when we watch Holmes perform his dance of deduction, he’s so specific and so certain that we’re lured by an innate love of closure into appreciating his clear train of thought and his “scientific” approach. He observes more details than most of us do, so who are we to challenge him? This notion, says Young, gets us into trouble.
Holmes is impressive because it’s easy with fiction to make him seem brilliant and always right. But since actual crime investigation is never this simple, Holmes’ type of reasoning could send investigators down the wrong track. You can look at almost any tale of false conviction and see the erroneous thinking, as Young does throughout the book. It’s what he calls “the Sherlock Effect.” He picks apart investigators for trying to be too much like Holmes.
The alternative – and apparent cure for the ills from the Sherlock Effect – lies in “forward thinking”: detectives first learn the incident facts from observable results and eyewitness reports. They look for consistencies and inconsistencies. Their conclusions rely less on assumptions and they use greater care to acquire as many facts as possible before deciding the result. They don’t assume that only they can fill in the blanks. “You can listen to an eyewitness with an open mind and see if what he says fits the clues,” Young writes, “but you cannot make up a story from the clues and expect it to be true.”
Listening should occur before surmising. Otherwise, one sets up tunnel vision and confirmation bias, not to mention risking the loss of evidence not noted because it doesn’t fit the schema.
Young ties a number of problematic investigative errors to the Sherlock Effect, using case examples like crib death diagnoses and child abuse. Yet he doesn’t actually prove with trend analysis or controlled studies that Sherlock’s methods are to blame. We don’t know that those who made the mistakes had any regard for Holmes, let alone set out to be Holmes. Even if the influence is simply due to exposure to a pervasive practice, anecdotes fail to establish the claim. In fact, Young oversimplifies Holmes’ approach, and readers who know the novels and stories will likely spot this weakness.
Massimo Piglucci, a philosopher who has long studied the Holmesian canon, describes Holmes’ method as a form of “eliminative induction,” because “deduction” is too limited to encompass it. Holmes, he says, actually works his way through inferences toward the best explanation by considering and discarding others. He uses whatever seems best for the occasion, picking “the right set of tools from a broad toolbox, depending on the characteristics of the problem at hand.” Holmes does use intuition, Piglucci observes, but he combines it with time-tested practices.
In “The Adventure of the Speckled Band,” for example, although Holmes makes quick (and potentially wrong) deductions about Helen Stoner when she tells him the tale of her twin sister’s death in bed, he doesn’t just take wild guesses about the chain of events leading to the death. He goes to the scene, researches their stepfather, examines Julia’s death room, ponders details from Helen’s eyewitness report, eliminates a hypothesis by testing the windows, asks about items in the room, corroborates his ideas about motive and MO with observation, and finally arrives at how and why Julia was murdered. It’s not exactly backwards reasoning based only on intuition. He does many of the things that Young thinks investigators should do.
There’s nothing wrong with forming a guiding hypothesis, as long as one stays flexible and accepts that it could change with new facts. The real problem lies with the arrogance of believing that one is always right or superior to anyone else, as well as deciding that someone is guilty before the evidence proves it. But this error is as easily attributable to an investigator's high need for closure, laziness, or poor training as to any Sherlock Effect.
Young would like to replace Sherlockian thinking with his own notions, in which one compares eyewitness accounts against evidence. He believes one can reasonably evaluate consistency and inconsistency, but this ignores a lot of cognitive psychology research that shows how easily different types of bias can infiltrate our evaluations. In some ways, Young is doing what he thinks Holmes is doing: believing that a simple formula ensures success. He criticizes others for “inventing simple and simple-minded hypotheses for vastly complex past events,” yet he invents a simple proposition for complex processes as well, just for different ones.
I agree that we should be careful about some of Holmes’ statements. One that I've found troubling is, “Any truth is better than indefinite doubt.” Really? Any truth? This pressures us to contrive an explanation that sounds right and achieves closure. That’s how many investigations mess up. Better to leave an investigation open than to tie it up prematurely with something that might seem true.
I also quake at this one: “When you have eliminated the impossible, whatever remains, however improbable, must be the truth.” As if any given investigator can think of all possibilities and effectively eliminate all impossibilities. What if they don’t have all the facts or don't realize the limits of their own imaginations? They might erroneously decide they’ve done everything possible when they haven’t. I’ve seen this, too. It’s the fallacy of believing that all the facts you know are all the facts there are.
To be fair, Holmes has some good advice, too, such as, “It is a capital mistake to theorize before one has data. Insensibly, one begins to twist facts to suit theories instead of theories to suit facts,” and “We balance probabilities and choose the most likely. It is the scientific use of the imagination.” He also claims that the “first rule of criminal investigation” is to “always look for a possible alternative and provide against it.” Young seems to agree with these ideas. So, Holmes is, at worst, a flawed role model. He’s not a wholly destructive force.
Despite the title, Young’s book is not actually a critique of Sherlock Holmes. It’s about today’s forensic practitioners who seem to adopt Holmes’ least effective style and who play well to juries that like Holmes-type reasoning. Young rightly claims that they’re doing harm. “What would happen if someone who was seemingly brilliant and had impressive credentials were to get up on a witness stand in a courtroom and engage in Sherlock Holmes-like behavior, weaving stories from clues? What if everybody on the jury believed that impressive expert? What if people were sent to prison because of that kind of testimony?” Young demonstrates how this happens and urges sweeping change. He thinks improvement requires erasing our devotion to an influential figure like Sherlock Holmes.
However, he must do more work to prove his point. Thinking like Holmes is neither necessary nor sufficient for making egregious investigative errors. Most of those that Young identifies are linked to attitudes – false confidence, arrogance, laziness, and lack of professional ethics. I do accept that made-up tales are poor sources for good investigation strategies, but the issues we see in forensic science today go well beyond a Sherlock Effect.
Young, T. (2018). The Sherlock Effect: How Forensic Doctors and Investigators Disastrously Reason Like the Great Detective. Boca Raton, FL: CRC Press.