Where the clothes are the person must also be: another lesson in logic


We balance probabilities and choose the most likely. – Holmes

Sherlock Holmes (Wikipedia)

As pat of the Senior Seminar, we discussed the reality that people don’t write out there arguments in logical form. Part of the brilliance of the Socratic Method was the use of questions to explore and probe a person’s view to expose the underlying assumptions, gaps, and contradictions that may exist.  Having looked at the hypothetical form of  a philosophical argument, let’s use The Adventure of the Noble Bachelor to practice identifying these arguments within a story.

The official detective was attired in a pea-jacket and cravat, which gave him a decidedly nautical appearance, and he carried a black canvas bag in his hand. With a short greeting he seated himself and lit the cigar which had been offered to him.

“What’s up, then?” asked Holmes with a twinkle in his eye. “You look dissatisfied.”

“And I feel dissatisfied. It is this infernal St. Simon marriage case. I can make neither head nor tail of the business.”

“Really! You surprise me.”

“Who ever heard of such a mixed affair? Every clue seems to slip through my fingers. I have been at work upon it all day.”

“And very wet it seems to have made you,” said Holmes laying his hand upon the arm of the pea-jacket.

“Yes, I have been dragging the Serpentine.”

“In heaven’s name, what for?”

“In search of the body of Lady St. Simon.”

Sherlock Holmes leaned back in his chair and laughed heartily. “Have you dragged the basin of Trafalgar Square fountain?” he asked.

“Why? What do you mean?”

“Because you have just as good a chance of finding this lady in the one as in the other.”

Lestrade shot an angry glance at my companion. “I suppose you know all about it,” he snarled.

“Well, I have only just heard the facts, but my mind is made up.”

“Oh, indeed! Then you think that the Serpentine plays no part in the matter?”

“I think it very unlikely.”

“Then perhaps you will kindly explain how it is that we found this in it?” He opened his bag as he spoke, and tumbled onto the floor a wedding-dress of watered silk, a pair of white satin shoes and a bride’s wreath and veil, all discoloured and soaked in water. “There,” said he, putting a new wedding-ring upon the top of the pile. “There is a little nut for you to crack, Master Holmes.”

“Oh, indeed!” said my friend, blowing blue rings into the air. “You dragged them from the Serpentine?”

“No. They were found floating near the margin by a park-keeper. They have been identified as her clothes, and it seemed to me that if the clothes were there the body would not be far off.”

“By the same brilliant reasoning, every man’s body is to be found in the neighbourhood of his wardrobe.”

Since most people don’t write out there arguments in logical form (which is not saying the argument is illogical), it is good practice to examine a portion of a narrative and write out the argument being made. Can you write the two arguments made in this portion of the story?

Lestrade:

hypothesis
observation
conclusion

Holmes points out that there is an unstated assumption Lestrade is making.

Holmes: restating Lestrade’s argument (in categorical form)

premise
premise
conclusion

Is Lestrade’s argument valid? Is it sound?

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