File this under the headline epistemology surrenders.
Rumsfeld baffles press with 'unknown unknowns'. On the subject of searching for terrorist threats:
"There 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. There are things we do not know we don't know," Mr Rumsfeld said.
"So when we do the best we can and we pull all this information together, and we then say well that's basically what we see as the situation, that is really only the known knowns and the known unknowns.
"And each year we discover a few more of those unknown unknowns."