It really comes down to your preferred definition of the word "know". Dictionaries offer several choices.
My favorite is this one:
Archaic . to have sexual intercourse with.
But more applicable here is this one:
To perceive or understand as fact or truth; to apprehend clearly and with certainty.
So, I guess if you are absolutely certain, you can say that you know, but that's still a subjective statement.
The only thing we can actually know with absolute certainty is our own existence. That old, I think therefore I am, thing. Everything else is a construct of perception.
My favorite is this one:
Archaic . to have sexual intercourse with.
But more applicable here is this one:
To perceive or understand as fact or truth; to apprehend clearly and with certainty.
So, I guess if you are absolutely certain, you can say that you know, but that's still a subjective statement.
The only thing we can actually know with absolute certainty is our own existence. That old, I think therefore I am, thing. Everything else is a construct of perception.