Why "razor"? Because it cuts away the unnecessary and redundant. Several Latin versions but this is the one I remember: noli multiplicare entia praeter necessitatem. Literally: "do not multiply essences without necessity" which is Medieval for "don't make your theory any more complicated than it has to be" or "the simplest explanation is the best". Or Newton (another Englishman, four centuries later): "Nature is pleased with simplicity, and affects not the pomp of superfluous causes". The modern American equivalent would be KISS: Keep It Simple, Stupid.
On the anniversary of 9/11 we were again inundated with theories about "controlled explosions". A great deal, if not almost all, of the "evidence" that 9/11 was an inside job is the presumed "free fall" of the buildings, jet fuel can't melt steel, thermite and many many other supposed "proofs" that the buildings were actually collapsed by a planned implosion. I have never found this convincing and am perplexed why so much energy is spent arguing back and forth.
A more productive approach is to turn the question upside down which is the practical application of "Ockham's Razor". "Turning the question upside down" is a technique I recommend. And there is much relevance to an intelligent and independent-minded assessment of the Western propaganda war: Litvinenko, Skripal, US election interference, Assad and chemical weapons. If the West really had evidence for its accusations, it wouldn't be relying on Bellingcat. Ockham's Razor slices off the nonsense.
The essence of the "conspiracy theory" conspiracy theory is that everyone is so busy arguing over minutiae that they never ask whether the fundamental assumption makes sense. Does it fundamentally make sense that Putin would try to kill Skripal years after he was traded? No it doesn't; so why are we arguing about perfume bottles? Does it fundamentally make sense that Putin would kill Litvinenko by such a convoluted and detectable way? No it doesn't; so why are we arguing about tea rooms? Does it fundamentally make sense that Putin would try to swing the US election without using his best information? No it doesn't; so why are we arguing about a ten minute meeting with a Russian lawyer? Does it fundamentally make sense that Assad would kill children with Sarin in the hour of victory? No it doesn't; so why are we arguing about holes in roads? The more we argue about perfume bottles, holes or tea cups, the more the lies stick. And maybe that's the intention: "The point of propaganda is to leave an impression after the details have been forgotten".
Ockham's Razor starts to cut when you ask yourself:
if it was a conspiracy, what is the simplest conspiracy?
9/11 is an illustration. Let's pretend that our Secret Hidden Masters decide that a "War on Terror" would be good for them and that an attack on some American landmark by Crazy Muslim Fanatics will start it off. Angry Muslims are set up; easy enough: entrapments are done all the time. The Masters figure out a way to control the planes because they can't be sure the dummies can or will do what what they're supposed to do. They block communications because passengers phoning to say the hijackers are panicking too would wreck the story. And, on The Day, the planes hit the Twin Towers, they burn out leaving a memorable and exploitable image: lower two-thirds white, black above: "Candles of freedom" "Re-Light Freedom!" "Remember the Candles!". The slogans write themselves. Chalked on bombs: 9 and two white stripes with black tops! Not too complicated: most of the people who could reveal the conspiracy die and the few others (who aren't already in "The Club") can have quiet car accidents off stage. A powerful effect at minimum exposure.
But suppose that one conspirator wants the buildings to come down. But this would be absurdly over-complicated: it takes a long time to openly prepare an empty building for a planned detonation; how much longer when you have to do it in secret? Every night you have to bet that several hundred people will notice nothing; every day you have to bet that several thousand notice nothing. They all know that the buildings were a target before and they will phone security. And if one person does, the plot is blown. Odds of millions to one, risking everything, for no discernible advantage.
Competent conspirators want their conspiracies to be simple, manageable and easy to execute. They want the risk of discovery to be as low as possible. Keep the buildings standing; it will serve the purpose just as well, or even better, and at a fraction of the risk. So, William of Ockham tells you to stop poring over videos: the controlled demolition stuff didn't happen because it would have added immense and unproductive complication.
And he tells us that Putin didn't kill Litvinenko by dribbling radioactive poison in every restaurant in London; he didn't try to kill Skripal by scattering a nerve agent randomly around Wiltshire; he didn't manipulate Americans "to get me out of the way", ignoring his most powerful weapon; Assad doesn't gas children to make his enemies attack him; Kerry doesn't actually have data on MH17.
It's not all that complicated once you think about the fundamental probability.
Noli multiplicare entia praeter neccesitam
What actually did happen? Who killed Litvinenko, brought down MH17, executed 9/11, what's the story on the Skripals? It's not our job to refute the Gish Gallop of accusations; the accusers are obliged to prove their cases. They have to prove them not by megaphone, petitio principii, Bellingcat's inventions or by starting other false hares; they have to use the same old boring methods that we used to see English detectives do in dozens of BBC TV series: evidence, argument, proof. So, less "Litvinenko: A deadly trail of polonium", more Miss Marple and Poirot from the BBC, please. To quote another fictional English detective who would be unable these days to get a job either in the BBC or in Her Majesty's Government:
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.
But I forget Ockham's Razor: these accusations are not the result of detection, they do not involve reasoning, they're Goebbels, they're not Holmes. Propaganda
(PS. I have referred to 9/11 to show that not all examples of petitio principii are done by the Establishment. It is depressingly common to assume the answer and remain in the bubble: confirmation bias, it's called.)