Friday, June 15, 2012

Game Research: Reverse Engineering a Holmes Deduction [VID]

I'm currently working on a computer game and a related research paper.  As part of this research, I'm trying to determine how Sherlock Holmes (in the stories) did his deductions.*  I'm working on putting this deduction algorithm into my game.

Perhaps the best way to do this would be to reverse engineer a deduction from a Holmes story.  For now, let's start with a deduction, actually a series of deductions, from the new series "Sherlock" on the BBC.

The particular series of deductions analyzed here come from the "Hounds of Baskerville" episode.

See the deductions from about 7:00 to about 10:45 in the clip.
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If the above video is no longer available, see also this YT video for a part of the deduction.

Text of the deduction:

SHERLOCK: Because of what happened last night.
WATSON: Why, what happened last night?
KNIGHT: How do you know?
SHERLOCK: I didn't know, I noticed.
You came up from Devon on the first available train this morning. You had a disappointing breakfast and a cup of black coffee. The girl in the seat across the aisle fancied you. Although you were initially keen, you've now changed your mind. You are, however, extremely anxious to have your first cigarette of the day.
Sit down, Mr. Knight,and do please smoke.  I'd be delighted.
KNIGHT: How on earth did you notice all that?
WATSON: It's not important...
SHERLOCK: Punched out holes from where your ticket's been checked.
WATSON: Not now, Sherlock.
SHERLOCK: Oh, please, I've been cooped up in here for ages.
WATSON: You're just showing off.
SHERLOCK: Of course, I am a show-off, that's what we do.
Train napkin you used to mop up the spilled coffee. Strength of the stain shows that you didn't take milk. There are traces of ketchup on it and around your lips and on your sleeve. Cooked breakfast, or the nearest thing those trains can manage. Probably a sandwich.
KNIGHT: How did you know it was disappointing?
SHERLOCK: Is there any other type of breakfast on a train?
The girl, female handwriting's quite distinctive, wrote her phone number down on the napkin. I can tell from the angle she wrote at that she was sat across from you on the other side of the aisle. Later, after she got off, I imagine, you used the napkin to mop up your spilled coffee, accidentally smudging the numbers. You've been over the last four digits yourself in another pen, so you wanted to keep the number. Just now, though, you used the napkin to blow your nose-- maybe you're not that into her after all.
SHERLOCK (continues): Then there's the nicotine stains on your fingers, your shaking fingers. I know the signs. No chance to smoke when on the train, no time to roll one before you got a cab here. It's just after 9:15, you're desperate. The first train from Exeter to London leaves at 5:46 a.m. You got the first one possible, so something important must have happened last night. Am I wrong?
KNIGHT: No.  You're right. You're completely, exactly right. Bloody hell, I heard you were quick.
SHERLOCK: It's my job.

Holmes makes six claims at the beginning.
  1. Something "happened last night."
  2. "You came up from Devon on the first available train this morning." 
  3. "You had a disappointing breakfast and a cup of black coffee." 
  4. "The girl in the seat across the aisle fancied you." 
  5. "Although you were initially keen, you've now changed your mind" about the girl.
  6. "You are, however, extremely anxious to have your first cigarette of the day."
"How on earth did you notice all that?"

Let's start with the second claim.  What line of reasoning brings Holmes to make that claim.  I've diagrammed the line of reasoning or argument below.
In this case, the claim is based on some keen observation.  The claim here is about travelling by train.  The deduction about coming on the first available train, is dealt with in latter deductions.

The third claim is a little more complicated.

This claim is based on two observations, common knowledge and knowledge of the time of day.

The fourth claim can be diagrammed as follows.
The above claim is based on observations and common knowledge.

The fifth claim...

The sixth claim...

There are new bases for claims here.  Again, we have observation, but we also have laws/rules and documents/data regarding the train schedule which apparently Holmes knows well.

And now back to the first claim...

While the above may not be perfect, it does give a clear sense of how the Holmes Method works.

So, in my computer game I want to give the player the ability to "do" the Holmes method.  The first, obvious thing that a player would need to be able to do is observe.  Observe or examine is a common ability given in computer games, so that would not be difficult.  An observe/examine action would result in the player getting information about the object, person, etc.  It also appears that the player will need to "know" certain facts and be able to access those facts (e.g., train schedules).  Perhaps a "recall" or "remember" action.   But, what other actions would there be?

To be continued.

* Yes, I know these are more accurately called abductions, but I thought I'd stay consistent with the words used in the Holmes stories.

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