Everything is an assumption, over time and through testing some are considered to be solidified as true, some are found to be false, and some remain uncertain. The only honest answer is "we think we know". However, because that is obvious and most likely true for everyone (unless you are (a) god) it is redundant. To say, "I know" is to say, "I think I know".
Is it an assumption that I know that I think I know I am reading your comment? I may not know for sure that you really wrote that, I only think I know that, but I DO know that I think this? Otherwise I wouldn't have wrote this in response to that since I wouldn't have known that I thought you wrote that with which to respond to it.
Therefor you can know that you think something, but not now that you know something.
The Creator of the Everything left His Guidebook the Holy Bible so we could know the truth. The Holy Bible has never been wrong. It is the most contested book ever written, yet it has stood the test of time.
Ugh, the website wont let me add a comment under my vote- i chose other;
We can only truly know; what we have experienced for ourselves, and even then, we tend to assume things. We can only assume that what we have seen or read is truth.
For example, if you saw your husband and another woman kiss, you could only assume he was cheating, you wouldn't know unless you were the experienced (either the husband or woman) (the woman could have forced kissed the husband, CPR, or any other situation)