What is Knowledge?

Yes, completely. Belief is something we do in our minds. You believe what you believe, I believe what I believe. We might believe many of the same or similar things, but they’re beliefs held by subjects. Hence believing is subjective.

And evidence can change from place to place.

It certainly can. I have often had the experience of being convinced that something is true(I still have milk in my fridge), for reasons that appeared to me very good at the time(I remember only using a little last night and putting the carton back in the fridge), only later to discover that I was wrong or mistaken when I got more evidence(the carton was empty). I would probably have claimed to know that I have milk in my fridge, and I’d then be wrong, and new evidence is what changed my belief.

Of course, the knowledge claim is only as strong or as certain as the evidence that supports it. My memory about last night just isn’t all that good, and/or maybe I’m just not all that good at evaluating how heavy the carton of milk is.

If proof that the knowledge can be justified to an absolute certainty is required for it to constitute knowledge, then nothing can be known. But it’s clear to me that different types of knowledge have different levels of support.

Think of a schizophrenic who has sufficient visual and auditory evidence to claim that all scientists he knows are actually reptilians in human skin suits. Why shouldn’t this qualify as “Knowledge”?

It does. He would claim to know it under my definition, yes.

Isnt it “Truth” that differentiates between false beliefs that one thinks is supported by evidence vis a vis actual facts of reality.

I don’t understand that sentence.

Are you suggesting that knowledge can be decoupled from reality?

Yes. You could claim to know something and be completely mistaken. The knowledge you have can hypothetically all be wrong. You could have a life’s experience of having been born, grown up, and lived in Australia, with billions and billions of remembered and every day accumulating evidences, and therefore claim to know with high degree of certainty that you are in Australia. And yet, you could be a brain in a vat. You could be in The Matrix, so all the things you think you know are actually wrong. You think you know how you were born, you think you know what the speed of light is, you think you know the color of the sky.
And it is possible that you could come to possess evidence that would falsify all your previous beliefs (things you would have claimed you know were true).

All knowledge is tentative and can be overturned with better evidence.

The sentence is simple. There are actual facts which are objectively true.

You are proposing a relativistic scenario where the absolute Truth cannot be really known. You are basically negating the concept of knowledge itself and replacing it with belief.
In your scenario, people really don’t know anything, they just have belief which they think is justified (on a purely subjective level)…

I agree, it’s just that I don’t think we can claim to know them with certainty.

No, I am saying we cannot be certain. Under normal circumstances, we cannot claim to be absolutely 100% certain that we have discovered what is the objective truth.

You are basically negating the concept of knowledge itself and replacing it with belief.

Not even remotely.

In your scenario, people really don’t know anything, they just have belief which they think is justified (on a purely subjective level)…

All you’re doing here is describing a definition of knowledge that requires certainty. I don’t see how we could obtain certainty in our knowledge.

That does not make sense to me.

Mathematics is not about reality.

Let me use a slightly different example.

I just looked out the window, and saw that it was raining.

Can I now say “I know it is raining.” I suppose I can, but it would be a lie. In all honesty, I can only say “I know it was raining when I was looking out the window”.

Yes, I believe it is still raining, though the rain is light enough that I cannot hear it hitting the roof. I’d say that I am justified in that belief. But I don’t see it as knowledge.

A belief, such as “It is raining”, is ephemeral. It won’t last long, because conditions change. It seems to me that “knowledge” ought to be a reference to something persistent, not to something ephemeral.

I have the ability to discern whether it is raining. I used that ability when looking out the window. And that ability is persistent. It is that ability, rather than a belief, that I want to take to be knowledge. And, by the way, it is that ability to discern that justifies my belief that it was raining.

I guess I am turning it upside down. I see knowledge as part of what justifies belief, instead of knowledge consisting of justified belief.