The case of the useful theory

“That fiend!” cried Holmes as he stared at the young woman’s corpse. It was not a pretty sight.

                I tried to console him. “Take comfort, Holmes. The police are hard at work on the case. They are trying almost anything. They have even consulted psychics.”

“You don’t believe in psychics, do you Watson?”

                “Well, I admit that none of them have passed any of your tests. However, it could be that your skeptical attitude blocks their abilities. That is, attitude may be a moderator variable: Psychic phenomena occur around people who have an accepting attitude but do not occur in the presence of people with skeptical attitudes.”

“Watson, I applaud your correct use of the term “moderator variable.” However, you have neglected to think about mediating variables. If a psychic is receiving and sending messages, how would that happen?   Where in the brain are psychic messages received and sent?”

                “You’re right, Holmes, psychics will never solve this case. But what about the police?”

“The police will never solve this case, Watson. “

                “But what about that new, energetic inspector—McGarretty—and the first-rate group of men working for him.”

“McGarrety’s ‘Book him, Slammo’ approach won’t work. His people have interrogated almost everyone on this island, and what do they have? Absolutely nothing, except reams of notes. The murders continue.”

      "But they’re collecting information. Facts decide cases, don’t they?”

“Watson, you surprise me. Certainly, facts are necessary. Just as one cannot build a house out of nothing, one cannot build a theory without facts. But facts mean nothing by themselves. Facts are only of value when you have some framework in which to interpret them. Pieces of a puzzle are only meaningful if you know where and how they fit. Thus, what may seem meaningless to others will often be an important clue to me.”

                “I see what you mean. You’re saying that McGarrety needs to formulate a theory to help him make sense of the mountains of data he has collected.”

“Precisely, Watson.”

                “But how could he get a useful theory?”

“Well, he could use induction to find a pattern. His men have interviewed hundreds of people, and the fiend has claimed 36 victims. If McGarrety would allow me access to his data, the police could have a theory!”

                “That’s not fair, Holmes. I hear they have a theory.”

“Theirs is not a real theory. They are simply looking for someone who resembles a crazed monster because they feel that the person who is killing these women must look like a monster. Their so-called theory has no evidence to support it. It is merely their own common sense. If Scotland Yard insists on following common sense, why don’t they use their common sense to realize that the killer is not going to look like a raving maniac? With London on edge, women are not going to allow themselves to be alone with someone who looks like a deranged killer. Furthermore, a person who has calmly killed victim after victim must be cunning and unobtrusive. What bothers me most about Scotland Yard is how they cling to this ridiculous theory. They refuse to follow other leads or to investigate other suspects. In addition, they ignore any evidence that contradicts this theory.”

                “Bear in mind Holmes that Lestrade is not blindly following Scotland Yard’s theory. I’ve heard he has his own theory that has some merit.”     

“I suppose you are referring to Lestrade’s speculations which he says account for all of the data. Have you read his so-called theory, Watson?”


“Why not?”

                “It is rather long.”

“Rather long is a gross understatement. Lestrade’s theory is 40 pages long. He devotes two pages to each murder. He has a different explanation for each of them and deduces that there are 10 different murderers. In short, his theory lacks parsimony. I’ll grant that Lestrade is well-meaning and thorough, but he doesn’t think deeply.  He is too caught up with the slight differences between the murders. If the murders aren’t exactly identical, he doesn’t think the same killer was involved. I, on the other hand, am convinced that there are definite similarities among all 36 cases. Although some victims were strangled and some were clubbed, all the victims were attacked from behind. To be fair, my hypothesis that these murders are not being committed by different people is a null hypothesis. As such,  it cannot be proven—it can only be disproven. “

                “Given that your null hypothesis can’t be proven, why do you believe it?”

“I am using it as a working hypothesis. Admittedly, I, like most scientists, when I do not have the facts,  may need to speculate. But know two things. First, my speculations are based on facts: all the murders occurred on dark nights when the victim was alone, and no men were seen by any subsequent passers-by. Second, I am quite open to finding evidence that will disprove my speculations. But to date, there is no such evidence. “

                “Very well, Holmes. Perhaps Lestrade’s theory needs to be revised. But you must admit that it accounts for the existing data.”

“A good theory doesn’t merely account for existing data. It must make testable predictions about the future. Ideally, a good theory would tell us when and where the murderer will strike next.”

                “Doesn’t Lestrade’s theory predict when and where the murders will occur?”

“Yes, his theory predicts that ‘the next murder will occur in London some time within the next two years. It’s laughable! How is that theory going to help anyone catch the murderer? The only person that theory will help is Lestrade. He may get a promotion because the fools at Scotland Yard will be impressed that his theory hasn’t been disproven. They don’t realize that the theory is too vague to be disproven and therefore is too vague to be useful. A useful theory would make specific predictions about the murderer’s behavior—predictions that could be tested. That way, if the predictions were wrong, the theory could be modified to become consistent with the fact. Eventually, we would have a theory that would allow us to trap the murderer.”

                “Why don’t you develop such a theory?”

“My dear Watson, I have done just that. I need only to refine it somewhat, and I’ll be able to lead this wretched villain into Lestrade’s waiting arms. If you will but give me a few days leave, I will have this sorted.”

        I returned to my surgery and left him to his theory.

        Two days later, I received a telegram, urging me to meet with Holmes at once. I cancelled my appointments, got my revolver, and was at 221B Baker Street in a trice.

        As I entered the sitting room, Holmes was speaking with a member of one of the most honorable families in England. I am sworn to secrecy as to her identity, but I can tell you that she was the most beautiful woman I have ever seen.

“Madam, this is my colleague, Dr. Watson. And Watson, you, of course, know this young lady. I was just discussing my new theory of the murders with her.”

                Our guest gasped and put her hand over her mouth. Then, her body convulsed, her skin turned a ghastly shade, and then she fell to the floor. I rushed to her aid, but it was no use. The poison had done its work.

 “I was afraid she might poison herself, Watson. Well, it is probably for the best. Her family could never have survived the scandal of a trial.”

                As I sat stunned, Holmes explained the whole story. With each murder, he had refined his theory. At one point, he made a major revision so that it fit with newly discovered facts. Eventually, he was able to pin down when and where the murderer would strike. He tried to convince the police of the validity of his theory but, as usual, they were blinded by their biases. Last night, he used his theory and a clever disguise to trick the murderer into attacking him. The murderer escaped, but Holmes was able to identify her. He then arranged for her to meet him at Baker Street.

                Thus ended the reign of terror of that most hideous villain, Jaqueline (Jack) the Ripper.

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