I realize the ambitious objective indicated by the title, but there's another perspective - the essence of knowledge, which is more limited in scope and can be more easily contained. And explained. I'm making this post to help me sort out some ideas I'm working on in my research in neuroscience.
What does it mean to know something? Is it to have that thing well characterized? To understand what might happen to it in most circumstances? Or all circumstances? To have access to the truth about a thing? I believe this last part involving truth goes beyond the scope of knowledge, and in doing so causes a great deal of confusion and grief. It's also the part of Plato's definition, (justified true belief) that was invalidated by Edmund Gettier in 1963.
If you've read my blog post, "Absolutely", you'll remember my description of approaching truth asymptotically, but never achieving it. Knowledge is that approach, ever waiting to be refined and edited.
Think about a few things that you "know" to be true. Are they really? Politics is a fertile field for knowledge. Half of any group will "know" things the other half dismisses. It's the same with religion. Conviction is no less "certain" from multiple conflicting perspectives. See what I mean? Half of what we "know" does not even approach the truth. And the other half is only a useful generalization.
The point is, what we "know" at any given instant is simply the best understanding available to us at the time, based on our own individual experience and perception, and in spite of our "conviction". Indeed, it may often be a long way from some objective and independent "truth". This is why it's best to always keep an opened mind.
Knowledge is a work in progress. To know something is only to approach its truth, and sometimes to fall well short. Yet we act on our knowledge because it's the best we have to work with at the moment.
Always be prepared to learn something new in your never-ending quest for knowledge.
