First I admit that I cannot define knowledge. But if you think you can define it, then I at least know more about it than you do. A popular definition is justified true belief. But then what does justified mean? Properly grounded? What constitutes proper grounding? And how is that properly grounded? You just substitute one synonym for another, and fall into either eternal regress, or circularity.
What we call knowledge may be nothing more than an illusion that facilitates the survival and procreation of those who believe it. Every legitimate declarative statement is either true or false. If you can identify which it is, you're more likely to survive.
Once we accept logic as reliable for determining truth, we can claim to know a whole lot of things. But how do we know logic is reliable? We don't know it by logic, because that's circular reasoning, which is a logical fallacy. We don't know it because it always works, because that's inductive reasoning, which is only good for determining probability. Just because something works doesn't mean your explanation of why it works is true - much less knowably true.
If knowledge is what we think it is, rather than merely a life supportive illusion, then it must be grounded in something transcendent to chemical events in brain cells. A personal Supreme Being would do the job. But I'm not going to say a personal Supreme Being is necessary, because I can't prove it to the satisfaction of most of my target audience.
That's as much as I can say without epistemic cop out. But rather than shut up, I will now cop out and keep on talking - just like the rest of the world. I claim to know what knowledge is. And I claim to know stuff. Those are epistemic cop outs, but I don't care. If I say there's a God, I can say he justifies my claim. If I say there is no God, I can still claim to know stuff, because I fuckin want to.
First I claim to know I exist, not because Descartes said so, but because I'm hard wired to know it. On the same level of knowledge, I claim to know that I think, perceive, and emote - have emotions. Any time I think, perceive, or emote, I know I'm doing it by hard wiring. On this level, chemical events in my brain are sufficient for knowledge, because they just tell me which particular chemical event I'm experiencing.
Second, I know logic is reliable, but not because I'm hard wired to. I know that because I'm programmed to know it. Didn't happen automatically. I had to learn it. But still, once I know it, it's part of my operating system. I can't possibly un-know it, unless my system gets corrupted.
There are no degrees of true knowledge; you either know something or you don't. But what we call knowledge has degrees and levels, because what we call knowledge is really a bunch of different things.
A statement is often said to be known by the impossibility of the contrary. That's wrong. Two contrary statements can both be false. A statement is known by the impossibility of the contradictory. That is the highest level of knowledge. It only applies to hard wired knowledge. Why doesn't it work for logic - programmed knowledge? I can't conceive of any universe in which logic is not reliable. But just because I can't conceive of something doesn't mean it's impossible.
So the second level of knowledge is inconceivability of the contradictory. Axioms are on this level. But we claim to know more stuff. What passes for knowledge is a hierarchy of certainty levels. I know the external world exists, and I'm not just a brain in a vat. I know it because if it were not true, it would make no difference to me. This is irrelevance of the contradictory. Better known as Leibniz' difference that makes no difference.
Next level: I know there is not a bulldozer in this room, because if there were, I would see it. This is imperceivability of the contradictory. Knowledge that comes of firsthand interpretation of data is on this level.
Next level: I know mermaids and centaurs don't exist, because I have never perceived evidence to the contradictory. And if there were such evidence, I surely would have seen it by now. This is ignorance of the contradictory.
Next level: I know bigfoot doesn't exist - or Loch Ness Monster. I have seen evidence to the contradictory, but I think it's crap. Conversely, I know the Holocaust happened. I have seen people who deny it, but I think they're full of crap.
The strongest label I could put on this level of knowledge is improbability of the contradictory. All knowledge that comes from other people's testimony is on this level - all historical events that I have not witnessed - all scientific experiments that I have not personally performed.
This is the sloppiest of levels. It contains a virtually an infinite number of degrees of probability, and no way to assign percentage numbers to most of them. This is the level that causes factual disagreements. It shouldn't even be called knowledge. But if we don't call it that, we can't compete in a world full of people who do.
Despite our best efforts, we are all epistemic copouts. But some to much a greater degree than others. There are real truth seekers, but many more truth obstructing game players who call themselves truth seekers, and no hard line between them. The degree to which we refuse to admit our copouts is the degree to which we become the latter.