The real argument the article makes is that no one seems to have proposed the theory until 1902. If it was generally a design consideration when the castles were built, we'd expect to have contemporary documentation of it.
I mean I can offer the same argument in reverse: if 70% of these staircases wound clockwise, they clearly favoured this orientation. How come we don't have contemporary documentation of the reason?
People were not stupid; if there was an actual technical benefit, it would have been known and shared, the same way that people knew and shared other castle construction techniques amongst craftsmen.
Tangibly, the absence of evidence for something can’t be magicked away by the “but what if they didn’t record it for a reason because it was a secret!?”.
If there’s no evidence, there’s no evidence. You can ponder all day, but it still boils down to, bluntly: there is no evidence that conjecture is correct.
If the swordsman theory were correct, it ought to be higher. Either it is really important that you can defeat invaders on stairs, and handedness matters for this, or it's not that big a deal and we can let some other consideration decide, for instance the descending stairs hypothesis.
So if was a big deal you'd think everyone would insist on having the stairs the right way, nearly 100%. If not there might be another weaker reason that leads to 70%.
I think 70% definitely tells you what kind of staircase was preferred assuming there are enough staircases (and assuming that that clockwise (CW) and counter-clockwise staircases had equal probability of surviving and being counted).
Assume there are 40 staircases, and that 70% (28) are CW. The binomial distribution tells us that the probability of there being more than 27 staircases that run CW is less than 0.83% if staircase direction is chosen at random.
Thus, the binomial distribution suggests that it is highly unlikely (<1%) that staircase direction was determined at random.
If you want to play around with the binomial distribution: https://www.wolframalpha.com/input/?i=binomial+distribution+...
The proper comparison is not a 50% cointoss, which is how you might think about some elections, it's a 100% world where every castle maker would tell their apprentices about this important CW swordfighting idea, and people who forget this are castigated for building an obvious weakness into their design.
The only reason it would be somewhat lopsided, but not decisively, is if there was some mild reason why people preferred one over the other, which is what your numbers actually suggest. Something like the "easier to walk down" hypothesis might make sense here, where for instance the CCW staircases are accounted for by aesthetic considerations like symmetry.
If 70% of surviving staircases are clockwise and they were built in similar numbers then there is clearly an advantage to the clockwise orientation. If they were not built in similar numbers, then its on the author to find a specific reason rather than simply reject the conventional wisdom on the subject.
You don't disprove something like this by pointing to a lack of evidence. You do it by finding compelling evidence for an alternative.
Archeology of 21st century man definitely states that 70% of adults used to eat burgers, then there is clearly an advantage to putting a piece of meat between two slices of bread. The bread must br protecting meat from rain and wildlife. People who put meat on top of bread have clearly died out in the evolutionary game. Even the few surviving specimen of men that put meat on top of bread, always cover it with cheese to confuse predators.
I mean, there is! It's easier to eat while holding. Meat tends to be a little wet, but bread is dry, so by putting meat in bread, you don't need utensils.
Romans built spiral staircases as well - did they favor a particular direction? What about other cultures unrelated to European castle building traditions?
Honestly, though, if you’ve ever worked on a construction project you would know: even if you had a record of a papal decree mandating that all staircases must turn to the right, multiple books documenting how to build staircases with a right turn and warning against left-turning designs, and original castle drawings showing the architect marked explicitly that the staircase must turn right, it would not be surprising to find that 30% of staircases turn left just because the contractor installed it backwards.
"This is my contractor John Mason, who likes to build right handed stairs." "And this is his son Mason Johnson, who hates his dad so he builds left handed stairs"
The author is making an "absence of evidence is evidence of absence" error.
He isn't making that kind of error. The burden of proof is on the people making the claim. Otherwise any sort of weakly plausible reason for choosing the staircase direction would be true because there is "only" absence of evidence.
Absence of evidence here means that while you can't rule it out, you can't positively state it either.
Right, so calling it a "myth", as in the headline, is incorrect. That would imply that you know it to be false. The author is taking the lack of evidence to mean that it can't be true.
And as for the burden of proof, as with any hypothesis, anyone is welcome to try to falsify it. I just don't believe that the evidence here has done that.
We think of monks as the only literate people in the past, but that was far from true. The common person might not have known how to read (I've seen good arguments they did a little, but I'm not qualified to evaluate them) but the rich did, and they hired scholars who could read to study things that were important to them. Any rich person who didn't have scholars studying military matters wouldn't last long in war as many seemingly obvious ideas don't work in real battles.
Quite the opposite, the theory he's questioning has no evidence, merely a good story justifying it. In the absence of actual evidence of the motives behind these designs, you should be agnostic, which is what the author is doing.
Are there many surviving documents outlining the reasoning surrounding each design choice?
I mean, you're lucky when you go looking in version control on a software project from the last couple of years if the documentation surrounding a reason for a design choice is anything more than 'fixed bug'. Expecting more detailed change control documentation from mediaeval castlebuilders seems optimistic.