Nicolaus Copernicus

"To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge."

"Of all things visible, the highest is the heaven of the fixed stars."

"Although all the good arts serve to draw man's mind away from vices and lead it toward better things, this function can be more fully performed by this art, which also provides extraordinary intellectual pleasure."

"To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge."