While I think that to say one knows something is to say one believes something, I think there are great difficulties in determining the difference between a belief and a true belief, let alone a true and justified belief.

The truth condition, in at least an absolute sense, is not possible to meet with any other belief other than, perhaps, "I know there is something rather than nothing" or "I know something exists".

The truth condition requires a check for the actual conditions of reality and no method we have, in principle, is capable of doing this.

What humans do have is science. But, science is a method that gets infected by politics, ego, and human ineptitude.

Science also only tells us about our proximal reality or, in other words, the reality we have empirical access to. Whether or not there is a world or worlds beyond what we have scientific access to is an open question that science can not answer.

And, scientific truths are often wrong in the decades and centuries following such truths.

However, I think it is important to look at the possibilities involved in a causal chain of reasons for a belief.

This causal chain is not impervious to deficits, but the idea is, perhaps, the best way to begin to distinguish, at least, degrees of certainty.

There are myriad problems with the idea of a causal chain but at least a commonsense psychological examination of the voracity of each link in the chain could help us to determine what things are viable for belief and what things we should throw out.