When you say "I know something X" do you ever think about how many times you hear "I thought I knew."

Answer 1

This is the fundamental issue for the branch of philosophy we call epistemology. What is knowledge?

Can something we conceive of (knowledge) even really exist? One way it has been attempted to be described is by saying there are two types of knowledge, "model" knowledge and "basic" knowledge. Basic knowledge is fundamental, and cannot be shown to be otherwise, while model knowledge is utilized by us as though it is the case...until we discover that it is not quite the case.

The problem is two fold, however, with this attempt. One is that even fundamental knowledge is called into question sometimes. The other, and more significant in my opinion, is that this explanation is a "cop-out" because it tries to split knowledge into two camps, even though our basic human experience (intuition) tells us that there can be one unified form of knowledge.

If you can resolve (or even further the understanding of) this dilemma, you will go down in history as a great philosopher.

Answer 2

I think that I didn't know your purpose of this question.