Philosophy’s history of reflection upon knowledge is a history of theses and theories; but no less of questions, concepts, distinctions, syntheses, and taxonomies. When I turned to to write my paper for me cheap, I learned that epistemologists distinguish about a dozen types and forms knowledge. So a single answer to your question does not exist, or it is worthwhile to clarify exactly what kind of knowledge is meant and to proceed from this with terminology.
There is actually a whole branch of philosophy dealing with knowledge. It is called epistemology.
Because it's possible that we know nothing.
What we think we know.