知与不知

“有一些众所周知的事情;我们知道一些我们知道的事情。我们还知道一些很明显的未知事情;那就是说,我们知道有些事情我们不知道。但也有没人知道的未知事情-----也就是我们不知道的未知事情。”
“There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we now know we don’t know. But there are also unknown unknowns. These are things we d...