So you fancy yourself a critical thinker. You get the importance of basing knowledge on evidence, but what constitutes GOOD evidence? Nearly everyone says they have evidence for all manner of claims. But evidence comes in degrees of quality, of certainty.
Belief should be granted in proportion to the evidence. If you think that Lord Vishnu answers prayers, including those changing reality, then wow, that changes everything we know about how the universe works! It’s a HUGE claim and that requires STRONG evidence.
So what’s GOOD evidence? There’s an order to it.
See also the Baloney Detection Kit
Evidence by Strength
Here’s a way to rank evidence.
1. The strongest evidence, by far, is something that can be measured. We don’t have to experience it with our senses since we have instruments that can measure stuff we can’t see. Wind, radio waves, light, intensity, gravity, etc. The coolest science, that runs the coolest gadgets, relies on the science of the invisible.
Look at how DNA tests can almost completely exonerate someone from a crime. But working with DNA testing, like all evidence, requires expertise. It establishes probabilities in a way that can say a particular blood sample is definitely *NOT* from a particular person but can only give probability that it *IS*.
2. Repeatability. Strong evidence will be clear to anyone with enough expertise to process it. A blood lab in China will get the same results as a blood lab in Miami, for example. When any knowledge assertion employs evidence that is testable by a broad swath of experts, it becomes a far, far stronger assertion.
3. Eyewitness accounts are the least reliable. They’re useful, of course, but with huge caveats. Courts increasingly realize that such accounts as not enough to convict.
http://www.scientificamerican.com/article/do-the-eyes-have-it/
A. Memories are imperfect. We construct stories that fill in blanks in a way that renders false memories as strong as the real ones.https://en.wikipedia.org/wiki/Memory_implantation
B. The context of our beliefs affects how we perceive. If you’re a Hindu who believes in Divas, you may see something unusual in the sky as one of these beings. A Hindu prayer meeting where people see an apparition will describe it in those terms. That’s why *JUST* having a lot of people see something may be completely unreliable.
Weak Evidence
Just because evidence is poor doesn’t mean its useless. But until stronger evidence is uncovered, the knowledge based on it must be considered appropriately suspect. It won’t be the type of knowledge on which to base consequential policy or action. If someone says there’s a meteor headed for earth it must be validated before we expend resources trying to act. If someone says the saw a premonition about it we should get confirmation before sending rockets.