sherlock logic


Marks and Rec: Misc #826

(Roman’s like, “what’d I miss?” But, y’know, referencing Hamilton even as he’s asking the question.) (Dialogue from Sherlock.)

The Lost Special: The One Way to Tie Up Every Loose Thread

In the last month this corner of the Sherlock fandom has thrown out a multitude of ideas for a narrative that could potentially resolve every last inconsistency in Sherlock series 4. Not knowing it, this community has debated different readings – all perfectly valid with only minor holes in logic – but have missed how they might all fit together into an intricate puzzle, each reading validating the other.

I have found one way to connect every loose thread.

Topics resolved include:

– EMP Theory vs “TFP as John’s TAB”: why both readings are meant to be exposed to the viewer (but we just found them too early)
– Benedict’s insanely long monologue they mentioned him having in Series 4.
– How another episode would only be comprised of a few new scenes
– Mary’s character development drifting far from her original plotline
– Moffat’s Doctor Who narrative that includes Toby Jones as a Dream Lord and what that means for Amy in “Amy’s Choice” and Sherlock in The Lost Special.
– How POVs intertwine in TFP, and how TPLOSH inspired the way The Lost Special would end.
– The entire bizarre nature of Series 4
– Breaking the 4th Wall
– The focus in The Six Thatchers on “The Duplicate Man”, “Twins”, “Two places at once”, and “Dead AND alive”.
– Three Garridebs
– Benedict claiming “Love conquers all” while Steven Moffat facepalms.

So if you want to know the one way this could all work, check out the rest of this post. But hear me out until the end, suspend your disbelief until you’ve finished, because regardless of whether or not you believe we’re getting The Lost Special, this reading which combines everything we’ve talked about for the last year is definitely arguable and until something else gets proposed, it is the one I’m sticking with til the bitter end.

Keep reading

Resources for the consulting detective

 11 Must haves for any aspiring consulting detective:

  • Notebook, preferably a pocket notebook. Used for writing down observations and theories. At the time, you’ll think “I don’t need to write this down, I’ll remember it”. You won’t.
  • Pen. Goes with your notebook. Pencils are ok, but it’s generally faster to write with pens.
  • Flashlight, preferably one with an assault crown. You never know who or what you’ll encounter whilst investigating a crime scene at night, but more importantly, you could potentially miss a lot of clues without the correct lighting.
  • Pocket knife, preferably one with multiple blade sizes, and a screwdriver. Used for cutting open sealed things, disassembling things (laptops, clocks, etc) that may contain clues, stabbing people, and freeing the zip cuffed prisoners of the kidnapper who you just rendered unconscious with your assault crowned flashlight.
  • A friend, preferably a helpful and willing one. They are good for bouncing theories, double checking chains of thought, picking up observations you missed, and bringing a second opinion
  • A phone. Preferably more than one, in the event of your capture, there is a chance your enemy may not think to look for more than one phone. Have your most important contacts on speed dial.
  • Combat boots, for rough terrain.
  • Gloves, combat and latex. Used for collecting evidence, as well as rough terrain.
  • Ziploc (or other airtight bags). Used for storing evidence.
  • Depending on the situation, food is never a bad idea. Make sure it is appropriate for the journey, avoid foods that can spoil, as well as sugary foods that will cause a sugar crash later.
  • A backpack or satchel, used for storing all of the above items.
Future plans

My parents: So what is your plan for the future?

Me: Watch tv series, and fangirl.

My parents: No, what do you wanna do with your life?

Me: Watch tv series, and fangirl.

My parents: What do you wanna do for a living?

Me: I want to get paid to watch tv series and fangirl over them.

  • Someone: *doesn't like something I like*
  • Me: How DARE they!
  • My brain: they are a different person with different opinions and views
  • Me: But why wouldn't they like it??
  • My brain: because they're a different person with different opinions and views
  • Me: but-
  • My brain: different opinions and views you dumb bitch
Logical fallacies

I was going to post the second “Thinkbox” today but I noticed that this might be more important. So I will list logical fallacies that most people fall into all the time. It is really important that these fallacies don’t cloud your mind when you try to make accurate deductions. If you, the reader notice that you may be a victim of any of these fallacies try to change your way of thinking.

Formal logical fallacies

- Anecdotal fallacy - To use personal experience as proof instead of statistics.
Example: “All women have long hair” because I’ve only met women with long hair.
A way to avoid: Realize that personal experience isn’t as accurate as statistics that have been done on many more people than you can meet.

- Appeal to probability - To think that because something is probable it’s also always the case.
Example: “You must be right handed” because most people are.
A way to avoid: The probability of something does never grantee you that it is correct.

- Conjunction fallacy - Assumption that an outcome simultaneously satisfying multiple conditions is more probable than an outcome satisfying a single one of them.
Example: “Linda is 31 years old, single, outspoken, and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations.
Which is more probable?
1. Linda is a bank teller.
2. Linda is a bank teller and is active in the feminist movement.”
Most people chose 2. But the probability of the two occurring together is less or equal to the probability of them occurring alone.
Pr(Linda is a bank teller) = 0.05
Pr(Linda is a feminist) = 0.95
Pr(Linda is a bank teller and a feminist) = 0.05 x 0.95 = 0.0475.
So the probability of her being both are lower than the lowest.
A way to avoid: Just because something seems to fit well together doesn’t mean it does. Try to think critically.

Informal logical fallacies

- Argumentum ad lapidem - Dismissing a claim as false without proof of its absurdity.
Example: “A: Atoms does not exist.
B: Why do you say that?
A: It’s ridiculous.”
A way to avoid: Don’t dismiss anything at first until you have researched the subject you think may be false.

- Argumentum ad ignorantiam - Assuming that a claim is true because it hasn’t been disproven.
Example: “A: Spirits exist.
B: No.
A: Prove that they aren’t real.”
A way to avoid: Don’t think that a hypothesis you have come up it true just because someone else can’t prove it wrong. Extraordinary claims require exceptional proof.

- Divine fallacy - You can’t imagine it to be true so it must be false.
Example: “A: Murder only happen in films
B: Why do you think that?
A: I can’t imagine anyone doing something so wrong.”
A way to avoid: Stop thinking that improbable is the same as false. Like the great Sherlock Holmes once said “When you have eliminated the impossible, whatever remains, however improbable, must be the truth”.

- Argumentum ad nauseam, argumentum ad infinitum - A topic has been discussed so much that is is seen as true or people don’t care anymore.
Example: “You have the left thumb over your right when your fingers are intervened. That means that you are right handed.”
A way to avoid: Stop accepting statements as true, conduct som research. Even if it’s on a small scale it might give you som pointers.

- Argumentum ex silentio - Conclusion is based on the absence of evidence instead of proper evidence.
Example: “A: Ah you are quiet so you did kill him.
B: But I didn’t say anything?
A: That’s why I know!”
A way to avoid: Try not to assume anything without evidence.

- Argumentum ad hominem - To attack a person instead of their argument.
Example: “A: I like ice cream.
B: Well you’re stupid.”
A way to avoid: You likely know that you’re doing this to some extent, so try to be a good debater and come up with a good counter argument. Or maybe just try to understand the other persons point of view.

- Onus probandi - To make a claim and think that other people must accept it or disprove it themselves.
Example: “A: Dogs always lick their owner when greeting them.
B: Not always.
A: Prove that they don’t.”
A way to avoid: Always try to prove your claims, it is your responsibility.

- Circulus in demonstrando - When you begin with the conclusion you’ll end up with.
Example: “A: I think he is right handed.
B: Why?
A: Emm.. Maybe because he has his watch on the left arm?
B: That doesn’t necessarily mean that.
A: It must mean that!”
A way to avoid: Try to observe first and make a conclusion based on the facts. Like Sherlock said “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”.

- Post hoc ergo propter hoc - Assumption that correlation is the same as causation.
Example: “He had an heart attack when riding a roller coaster, so that means I will have one on the roller coaster too.”
A way to avoid: Think about the problem you have, does the correlation really equals causation?

- Fallacy of composition - To assume that the whole is true because a part of it is true.
Example: “All cells are aquatic. Therefore all organisms (which are composed of cells) are aquatic.”
A way to avoid: Like earlier, try to be critical and don’t accept something as true without research.

- Black or white fallacy - Two statements are held to be the only possible option, when in reality there is more.
Example: “The coin can only land heads up or tails up”.
A way to avoid: If you are used to problem solving this shouldn’t be to much of a problem. Try to keep an open mind when solving a problem.

- Fallacy of the single cause - Assumption that there is one simple cause of an outcome when in reality it may have been caused by multiple events.
Example: “She has a fear of spiders because she had one in her hair when she was young” When it may have been more that contributed to the phobia.
A way to avoid: Don’t assume that everything is caused by one event, try seeing the whole picture.

- Psychologist’s fallacy - Presumes you can be objective in your judgement.
Example: “A: Something will happen to you if you go out this late.
B: You only say that because I’m your daughter.”
A way to avoid: This is something that is hard to avoid, we as humans will always be biased when it comes to things we care about, so try breathing and think calmly about the problem you wish to solve if you can’t ignore it.

Even though you know these fallacies they will still affect you. No human can get rid of them all, “errare humanum est” (to err is human). But being aware of them hopefully helps you think about the problem you face a bit more.
The ones you should be most aware of is:

Anecdotal fallacy.
This I see all the time. People think that their own experiences must be what everybody else is experiencing too. This is a problem when reading studies and the results of the studies doesn’t correlate with your own experience, so you don’t believe it as much.

Appeal to probability.
Something that people new to deduction often seem to think is that it’s always foolproof. That even though most things in deduction is statistically based it must come true all the time. This isn’t the case, and new people discard deduction as something they cannot learn or something that is false and that’s tragic.

Argumentum ad lapidem.
If you as a deductionist disregard a fact as false without proper evidence you may have trouble learning the art of deduction. Being critical is good but to disregard it entirely isn’t.

Argumentum ad ignorantiam.
Likewise assuming that a fact is true because it can’t be disproven seems to be a trend in the world of deduction. I am still baffled by how many people think that long fingers is connected to piano playing (it’s the fingers flexibility that is connected to it.)

Divine fallacy.
This falls into the same category as the two above.

Onus probandi.
If you have come up with something then it’s also your responsibility to prove it to be right, if you care about it being proven to be correct.

Circulus in demonstrando.
My students in deduction have all done this mistake at least one time each. Try to observe then make deductions.

Post hoc ergo propter hoc.
Correlation does not equal causation.

Fallacy of composition.
If a deductionist have some parts of deduction figured out, well that doesn’t mean they know everything.

Black or white fallacy.
Most of the time it exists more than two options, your job as a deductionist is to figure out which of the options is more likely.

Psychologist’s fallacy.
Don’t ever believe yourself to be completely objective.

And with that, I’ll see you my irregulars.

The Laws of Deduction

In deduction, we use logic and generalisations to come to conclusions, or deductions about a thing or person. Many people do this subconsciously, little things like what hand someone writes with or if someone gets engaged, but never takes it to its full extent.

Of course, we all know Sherlock doesn’t use deduction. He uses a mixture of all three types, Deduction, Induction and Abduction, things we are writing posts on right now.

Deduction, however, is a science, and as with many others, has laws, things that cannot be broken and still have your conclusion come out as true. These laws are easy to learn and can help stamp out any incorrect deductions you may make, just by running them through the three of these:


From Modus ponens, the Law of Detachment basically means if a conditional statement and a hypothesis are made, a conclusion must fit both to be true.

The Latin, Modus ponens, means “the way that affirms by affirming” which basically explains the entire concept. Put simply, “if X implies Y, and X is true, so must Y”

  • X=Y is the conditional statement;
  • X as the hypothesis;
  • Y as the conclusion.

An example of this is:

  • If someone is right-handed, they will write with their right hand
  • Someone is writing with their right hand
  • The person is right-handed.

Pretty simple concept, and very useful.


Syllogism comes from Greek, and it means conclusion or inference. You have probably seen an example of it before, in the form of:

All men are mortal
Socrates is a man
Therefore Socrates is mortal

So what does it mean? Well, simply, a hypothesis of a statement combined with the conclusion of another. In the example, hypothesis 1 (H1) is “all men are mortal”  hypothesis 2 (H2) is “Socrates is a man” and if you combine H1 with the conclusion of H2 then we reach the conclusion of “Socrates is mortal” which is correct, in this case. Simply:

  • X = Y
  • Z = X
  • Z = Y

However, this law isn’t always true. There can be times when your conclusion isn’t valid, for example:

Some televisions are black and white
All penguins are black and white
Therefore, some televisions are penguins

Clearly, this is wrong. A way around this is to not form hypotheses that have no conclusive proof, only use ones that have been accepted by the majority of people, and don’t try to combine incompatible hypotheses, and also, the law itself does not have flaws, the logic is there, and it’s your responsibility to make sure YOUR logic is sound when you use this law.


This has the longest title, but is the easiest concept to understand. Contrapositive also comes from Latin, this time Modus tollens, meaning “the way that denies by denying”  the concept basically states that if a conclusion is false, so must the hypothesis.

Again, an example:

If I am lonely, there is nobody around
x, y

There are people around;
I am not lonely.

x = y
Opposite of x = Opposite of y

Another pretty simply rule, but you can see that it’s true.

And that’s it, the three laws of deduction: detachment, syllogism and contrapositive. You do not need to learn them all, but if you are planning on making deductions that heavily involve hypothesises, then I suggest asking an effort.

Technically, these are laws of logic, but many places I researched them put them down as laws of deduction, so whilst the name of them is to be debated, I’m confident that they work and are sound.

Any questions or corrections feel free to send an ask.