A way of fiddling statistics
where you don't establish the conditions until after you've "proved" them. The prototypical example is of a person shooting a gun at a wall, then painting a target around the bullet-hole, and claiming to have scored a bullseye.
Karl Popper summed up this fallacy as applied to science with "A theory that explains everything, explains nothing". Basically, if any possible outcome could be interpreted as supporting the theory then it is useless. Which is the pretty much the same thing as the concept of falsifiability
- Displayed by recent apologists for Joseph McCarthy such as Ann Coulter, who claim that the Venona intercepts declassified in 1995 show that McCarthy was quite right. In fact, the Venona intercepts only mention a single one of McCarthy's accusees, Mary Jane Keeneynote , and not for what McCarthy accused her of. McCarthy said she was a communist party member...which distracted from the fact that she was an actual GRU spy. This is somewhat akin to the fallacy in the sense that his supporters claim that the fact Keeney was accused by McCarthy and was guilty of spying (the only individual called before McCarthy who was) shows he was right; in fact, it shows he had no idea what he was doing and stumbled over Keeney by dumb luck...and even then he didn't catch her and quite possibly derailed real inquiries into her. Nice job, "Tailgunner"...
- The so-called "Bible Codes" use this fallacy. Rather than saying what they expect to find in a particular book beforehand, the people who produce these simply manipulate the letters until they find something that they can use. Words count regardless of whether they run up, down, right-to-left, left-to-right, diagonally, or even have the letters adjacent at all.
- This particular case was specifically shot down by a skeptic in a History Channel documentary about such Bible Codes. To prove that such a "spectacularly rare occurrence" actually was more likely than people were willing to admit, he applied the principles for finding codes to Moby-Dick, looking for "predictions" of the assassination of JFK. He found quite a few. As with the metaphor of monkeys with typewriters, any sufficiently long stream of data, if looked over using enough different formulae, will produce words or phrases that correlate to some kind of event that occurred after that book was written.
- John Safran vs God put this exact argument against the Bible Code to the test by feeding the entirety of Vanilla Ice's back catalogue (song lyrics and liner notes) into the decoder; even "Ice Ice Baby" is able to turn up 9/11 "predictions." Then they took the 9/11 Comission's report and used the code to find references to the fall of Vanilla Ice's career.
- Shakespeare's works get this treatment too. Some who dispute the authorship of his plays claim messages hidden in them reveal the truth when the right cypher is applied.
- The same is said about the Bible, claiming examples prove that Shakespeare wrote the Bible.
- Similarly, interpretations of the metaphorical elements of Nostradamus' prophecies may be seen as examples of this fallacy.
- There have been documentary programs on Nostradamus' prophecies where the proponents of Nostradamus' prescience do things like add and subtract numbers or alter letters in order to interpret things he wrote as referencing WWII. People have also pointed out that it's strange how Nostradamus' prophecies only seem to be understood to apply to something after the event has happened, which is also indicative of how this trope ties into Confirmation Bias. Nostradamus was a genius who was able to predict the future, yet no one predicted WWII from his writings. After WWII, people went back over his works and went to great lengths to prove to themselves that Nostradamus had predicted it. In reality, the passages could be interpreted or twisted to be applicable to anything one desired.
- Likewise, all claims of various people's names being secret encodings of the Number of the Beast, 666. There are a lot of ways you can assign numbers to letters or words — try enough of them, and you will find one that adds up to "666".
- This one is actually referenced in War and Peace, where Pierre plays around with Napoleon's name and titles to make it all add up to the Number of the Beast, then does the same thing to his own name to "prove" that he's destined to assassinate the man.
- This concept is parodied in the Nostalgia Critic's review of End of Days.
- Basically, the film The Number 23 runs on this. Once you start looking for 23 (or any other number) in creative enough ways, you'll see it everywhere.
- This is spoofed by The Number 24.
- Also spoofed on one episode of Aqua Teen Hunger Force in which Frylock becomes obsessed with the number 100. His explanations quickly devolve into combining completely arbitrary numbers with no rhyme or reason until he eventually just adds exactly what he needs to get to 100 without explaining why. Even Master Shake realizes that he's just pulling things out of his ass.
- Beautifully illustrated in the Principia Discordia with the Discordian Law of Fives: "All things happen in fives, or are divisible by or are multiples of five, or are somehow directly or indirectly appropriate to five."
- The Illuminatus! Trilogy, being heavily influenced by Discordianism, further deconstructs this. After playing up the significance of the Law of Fives throughout the book, Hagbard Celine then proceeds to demolish it by explaining it as an example of this trope, reinforced by intellectual pareidolia. He goes even further, explaining how even the number five is merely an accident of nature: "If humans were born with six fingers instead of five, we'd be talking about a 'Law of Sixes'".
- In Planescape: Torment, Morte mentions the "Rule of Three", a popular underlying principle of the Multiverse. He then criticises it and explains that if you ascribe importance to any number, you're bound to find evidence for it. It's also a good example of the Fallacy Fallacy. Planescape is a setting which runs quite literally on Clap Your Hands If You Believe, and the planes themselves warp in response to belief. In one case, it's so strong that a man is convinced he does not exist - and stops existing! As a consequence, many people believing in the Rule Of Threes is evidence that the Rule Of Threes is real in that setting.
- In the lead-up to the 2012 American Presidential election, there was much to do that a mathematician had found an algorithm that predicted the winner of every Presidential election for the past 50 years. Being on this page, obviously he took the raw data and simply found one that fit it.
- Malcolm Gladwell's notion of the "tipping point"; tipping points are points after which change is perceived to have been inevitable, but since they are only recognisable as such after the fact, you can't predict them in advance, so all they're good for is making the person talking about them look smart. (Tipping points are observable in natural phenomena; for example, the boiling point of water at sea level is 100C, so you can predict that when water gets to that temperature at sea level, it will boil. Anything more complicated than that and you're getting involved in probability theory.)
- Discussed in π, when Sol criticizes Max for obsessing over the number 216. He says that Max will soon see 216 everywhere he looks because he wants to see it, lowering himself from mathematician to numerologist.