I still don't see a meaningful distinction between a conspiracy theory and what
@Ovation called plausible speculation, as the latter does not have any hard evidence, either.
As I said, the term "conspiracy theory" carries the implication of a specific mindset. The difference is how the proponents respond to a challenge. Someone offering a plausible speculation will keep an open mind and change their opinion if new evidence disagrees with it. They admit it's just conjecture and don't invest in it as something they need to believe. A conspiracy theorist will double down on their belief and see the contradictory evidence as proof of an even greater conspiracy to hide the truth. The reason it's called a conspiracy theory is because conspiracy
is the theory. It's not just a theory that a conspiracy is happening. It's a mentality that defaults to conspiracy as the preferred theory for explaining anything, and that is therefore immune to rational counterargument because anything that conflicts with the conspiracy theory will automatically be interpreted as a product of the conspiracy itself. If your guy didn't win the election, the election must've been tampered with. If a hundred independent recounts confirm the votes were not tampered with, then all hundred separate groups must have been agents of the Deep State. And so on.
But we're getting off the subject. Your question was how to distinguish between a valid and an invalid theory in the absence of evidence. My answer is that
you don't. You don't need to rush to pick an answer before you have evidence to base it on. You just keep an open mind and wait for more input. This is what conspiracy theorists don't do. A rational speculator will see lack of evidence as reason to assume nothing. A conspiracy theorist will see lack of evidence as a license to assume their wild guesses are correct. So don't do that. Don't assume you have to decide right away whether a hypothesis is right or wrong. Just wait and see.
And, of course, the credibility issue is very subjective, as well, and can easily be used against the truth. As all politicians know, if you can't truthfully argue against a narrative you don't like, it's easier to attack the credibility of the source of the narrative.
No, credibility is not subjective to a rational observer who knows how to assess claims critically in light of evidence, reason, and evaluation of the source's potential bias. Yes, any demagogue can attack the credibility of an opposing viewpoint, but a listener who knows how to think critically will be able to penetrate the flaws in that demagogue's rhetoric and identify the agenda behind their arguments, so that you can tell their attack on others' crediblity is itself not credible and is merely a deflection from their own dishonesty. You
can tell the difference. This is a fundamental part of how historians interrogate historical sources, how competent journalists assess the legitimacy of their sources (as opposed to "news" shows that just want talking heads to shout at each other for ratings), how juries assess the credibility of testimony, etc. It's not just one person's word against another. You can assess whether their arguments make sense, whether they have an agenda behind them, whatever.
For instance, just yesterday I was looking into the question of whether it was okay to keep using the low-cholesterol butter substitute I use or whether its health claims were exaggerated and it would be better just to switch to butter. I found a site saying the substitute was terrible and unhealthy, but it was written with intense emotion and using scare words like "Frankenfoods," so I didn't trust it. The writer was obviously intensely emotional about the subject, and thus they were more likely to try to twist the evidence to fit their strong bias than to offer a conclusion based honestly upon the evidence. They also wanted to use emotive rhetoric to scare and anger people rather than giving them information they could consider rationally, which made them even more untrustworthy. Conversely, I didn't bother to click on the links that came from the product's manufacturer, because they obviously have a vested interest in convincing me their product is good and thus their assertions cannot be trusted to be objective. The sites I was most willing to listen to were the ones without a dog in the fight, things like consumer news sources that looked at both sides of the issue and offered a balanced report without an obvious agenda or fearmongering rhetoric. They pretty much said that there's nothing wrong with using either butter or the substitute in moderation, and both have different advantages, so it's up to the individual.
One of my history professors liked to say that anyone who claims to be absolutely certain of anything is trying to sell you something. The people you can trust are the ones who
don't insist they're undeniably right and you have to believe them at all costs. Everyone has a bias; honest people try to recognize their own biases and disclose them so that others can take them into account.
