"As we know,
There are known knowns.
There are things we know we know.
We also know
There are known unknowns.
That is to say
We know there are some things
We do not know.
But there are also unknown unknowns,
The ones we don't know
We don't know."
-- Donald Rumsfeld
Feb. 12, 2002, Department of Defense news briefing
"The only true wisdom is in knowing you know nothing."
-- Socrates
To me, Rumsfeld's musings is not only a clear example of the kind of statement public officials should never make because it is so internally complex that it leaves the listener completely perplexed, but it is also interestingly incomplete.
Let's assume its complexity is self explanatory, so I will deal with the incompleteness.
What he is trying to do, is to enumerate all combinations of facts that are {known, unknown} and the state of our knowledge about the facts.
We can construct a table of all combinations and fill it in with Rumsfeld's quotes, like this:
What we know about our knowledge of the facts | ||
We know if we are informed or not | We are not aware of the question | |
Known facts | There are known knowns. There are things we know we know. | |
Unknown facts | There are known unknowns. That is to say, we know there are some things we do not know. | [...] there are also unknown unknowns, The ones we don't know we don't know. |