This is exactly how science works. It self corrects as new information becomes available.

At least 4.

when science backs it up.

I’ll colloquially use the word “fact” for extremely well supported claims, but in my head the only actual “facts” are mathematical derivations. Evidence supports the veracity of a claim, and a claim with a lot of evidence gets a tentative place in my world model, but any of those claims can be refuted by sufficient counter-evidence

really depends on the source and if it makes sense in the first place.

When a lot of people who have nothing to do with each other say the same thing.

When people who dedicate their life to this one thing say the same.

When I can come to the same conclusion based on the reasoning behind it

When it is repeatable.

Then I going to accept it as a fact otherwise it is just something someone has said.

A couple kilobites, minimum.

It varies widely depending on a combination of whether it impacts me directly, whether it contradicts or is inconsistent with information I have already accepted as fact, and the source. The source includes being reliable and if the fact could be something that serves the source’s self interest as that would require corroboration.

Until recently, if NASA tells me their current data shows that black holes exist at the center of a galaxy I take their word for it. They have been consistently reliable for decades and their entire mission is about increasing knowledge and sharing it with the entire world. With recent administrative changes I am more skeptical and wouldn’t trust something that contradicts prior scientific discoveries without corroboration from an external agency like the European Space Agency. I would take the ESA at their word currently.

If a for profit company says anything I want corroboration from a neutral 3rd party. They have too much incentive to lie or mislead to be trusted on their own.

Something from a stranger that fits into prior knowledge might be accepted at face value or I might double check some other source. Depends on how important it is to me and whether believing that would lead to any obvious negative outcome. I will probably also double check if it is interesting enough to want to check, and I’ll use skepticism as an excuse.

That covers actual factual stuff that could possibly be corroborated by a third party. Facts like the Earth orbits the sun or Puerto Rico is a US territory type stuff.

Then there are other things that can be factual but difficult to determine and that is a combination of experience and current knowledge, plus whether believing it would be a benefit or negative. If someone tells me the ice isn’t thick enough based on their judgement I will treat it as a fact and not go out on it unless I had some reason not to believe them. If they told me apples were found to be unhealthy I would check other sources.

Hume had something like the wise apportion their confidence to the evidence, and Carl Sagan’s extraordinary claims demand extraordinary evidence can apply. So if those are true the quality and type of data is going to depend on the claim of fact (friend says they bought a dog vs a dragon), and the amount of evidence depends on the claim and your general standard of evidence. If you’re lowering or raising your standards for a specific claim that’s usually going to mean there’s a bias for or against it.

tl;dr 42 pieces of data

It honestly depends more on the source to me. I’d like to claim to rely on data but life is short and there is no way I can verify even a fraction of all the truths I have come to accept.

A sufficient amount

I’m not sure how I would even quantify this.

But I could qualify this: having a consensus across multiple trusted sources.

If it’s a really reliable source and sounds plausible, very little. Iran hit a hospital in Israel recently.

If it’s some random person and sounds plausible, probably many repetitions from unrelated people in unrelated contexts, with some time as “word is” after a couple or few mentions. Airport security is theater and misses actual weapons all the time. I guess I should add the caveat that if it’s something easily refuted like “TSA hires out of malls” it gets promoted to fact faster, because of Cunningham’s law.

If it sounds implausible, a lot. Like, it might be a thing I painstakingly confirm or deny over the course of years. Thermodynamics is always explained in a way that has massive gaping logical holes. It obviously empirically works, but a rigorous derivation without any sneaky tricks would probably imply a proof of P!=NP - and it took me years to work my way through enough papers and literature to confirm that.

If it’s a source or type of source with a history of making up the sort of thing they’re saying, infinite - it will be all noise regardless of how much data there is.

Laying it out like this, I clearly put a lot of emphasis on the motivation and past track record of sources. There’s so many things to see and measure, far too many, and there’s also lies and mistakes, so I guess one has to. That’s probably been true since the stone age, and probably drove some human evolution, although it’s intensified quite a lot in recent history.

Note that even facts are still subject to skepticism, discussion and revision. Absolute certainty it it’s own beast, and it’s not a universally agreed-on fact that it even exists.

ill tell you this, the amount of data would require for anyone accept a statement or idea as fact is related to their emotional assessment of the idea. See it all the time with trump supporters that think that trump is actually fighting to cut tax on overtime pay simple because he said it on the trail and there no evidence (and they have no evidence) that is happening, on the other hand it would take an infinite amount of evidence that trump took bribes even as he openly appointed Elon after spending millions of dollars.

so its weird that you have to propagandize the facts just to get people anywhere near a reasonable level of skeptism.

but for me I just say anything is valid unless I know how its wrong, which is limbo of acceptance then afterwards it can become a scoreboard where for and against. maybe a source doesn’t 100% line up with a statement, hell even video/audio evidence can be incongruent with a statement (as in its similar to what’s said but doesn’t back up a statement). I think the claim that Floyd overdosed but the video doesn’t show a overdose from opioids, so you’d have to rule out overdose simple because video doesn’t match the description of an overdose.

it wouldn’t take much, generally new information has to be consistent with what I know. the hard part is understanding the new information. no one is randomly disprove gravity or that things have mass, but someone can prove to me how a myth is meant to be interpreted for the intended audience

Basically, if it’s in the Bible, it’s fact. Everything else is entirely made up by the devil.