In my experience, there are limits to what most people will believe. There are things that will strain the credulity of all but the most credulous, and this is entirely separate from the usual rejection by some of conventional explanations for their pet belief.
To reiterate the title of this post, what is evidence? At its broadest and most basic level, it is simply any form of information that gives you a reason to accept something as true, a ‘sign’ if you will. It doesn’t have to be Proof™, much less absolute, concrete, or merely tangible.
But it must be something that you can directly or indirectly perceive.
People tend to have different heights for their personal bars for evidence, many
typically having a much looser concept of evidence than others, each differing on how sound evidence must be before considering a claim of fact valid. There’s no finely divided line between, no clear dichotomy, of believers and skeptics, but a spectrum.
The requirement for evidence as a condition of an acceptable statement of fact is far from closed minded; it’s good science, good philosophy, and good thinking. Consider if this were not so, and if belief alone were a requirement for to prove a claim.
Imagine being in a court of law – say you were accused of a serious crime, serious enough that it would be very unpleasant if you were to be convicted. Imagine further that you are innocent, and that there is evidence for this. Now, let’s just say for the sake of argument that the jury in this case is more likely than not to convict a defendant accused of particularly heinous crimes.
Now, do you really want that jury to convict you on the grounds of their belief without evidence that you are guilty? Or would you rather they examine the evidence that you are innocent, evidence which would exonerate you and allow you to go free?
Personally, my money’s riding on the jury looking at the evidence rather than the
groundless (in this case) belief in the defendant’s guilt.
What is not evidence by the standards of science? Well, for one outstanding example, most anecdotes, for starters. Why? Because such accounts are sometimes secondhand and often further removed from the listener, and even if not, the listener has no direct, independent access to the events recounted, no matter how honest, intelligent or well-meaning the speaker is, there is always the possibility of omission, exaggeration, or other errors concerning key details in the account, becoming more so the further removed it is from the original source. There’s here the danger of a game of Chinese whispers going on.
This is simply the result of the inherent flaws in memory and perception, and our often flawed interpretation of what we perceive, that we all have as humans.
At best, in science, anecdotes are only useful as a starting-point for the construction of a hypothesis, a beginning point for further inquiry, they are, unfortunately, not suitable as a means of testing a hypothesis, for if used that way, they can erroneously lead you to believe any conclusion you want to be true, especially if it isn’t.
Philosophers of science and logicians almost mostly agree that evidence in the
scientific usage of the word is always provisional, and that any explanation it is used to support must also conform to at least one or more criteria of adequacy to be valid, such as testability, fruitfulness, scope, simplicity, and conservatism.
Also, in science, the evidence for any claim must be obtained by sound methods – the means and ways used to conduct any test of an idea – and for the more probabilistic sciences, sound statistical methods, and if not, the evidence gained, such as it is, is simply not valid.
As you can see, not everyone has the same personal criteria for evidence, but modern science has very clear guidelines as to what constitutes evidence, and any data offered must pass the gauntlet of sufficiency, not just necessity, to be acceptable, and thus to expand our knowledge, for the time being, of the universe.