What do you know that has never entered your mind? Quite a lot, it seems.
Consider some thoughts that have never entered your mind: Pythons in yellow tutus cooked into a devil’s food cake! Obsidian nostril hairs that vibrate to the frequencies of your favorite R&R radio station! I’d bet these ideas have never before entered your mind. But just thinking about them doesn’t mean you “know” them. They’re just strange thoughts.
But consider this: have you ever thought about George Washington’s grandmother? (If you’re a historian who has, pick a grandmother from the 18th Century you haven’t thought about.) Think about this, too. Washington’s grandmother was born before yours! You know this to be true! In addition, you know that Julius Caesar’s grandmother was born before both grandmothers already mentioned. But it is highly unlikely that you have ever entertained such thoughts before in your life.
Isn’t it true then that there are billions, possibly, of things that have never entered your mind but nonetheless you know them?
To examine these issues further, see Conditions of Knowledge