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"There are known knowns" is a phrase from a response United States Secretary of Defense Donald Rumsfeld gave to a question at a U.S. Department of Defense news briefing in February 2002 about the lack of evidence linking the government of Iraq with the supply of weapons of mass destruction to terrorist groups.
Reports that say that something hasn't happened are always interesting to me, because 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. And if one looks throughout the history of our country and other free countries, it is the latter category that tend to be the difficult ones.
The statement became the subject of much negative and positive commentary.
As for the substance of his statement, Rumsfeld's defenders have included Canadian columnist Mark Steyn, who called it "in fact a brilliant distillation of quite a complex matter", and Australian economist and blogger John Quiggin, who wrote, "Although the language may be tortured, the basic point is both valid and important ... Having defended Rumsfeld, I'd point out that the considerations he refers to provide the case for being very cautious in going to war."
Psychoanalytic philosopher Slavoj Žižek says that beyond these three categories there is a fourth, the unknown known, that which we intentionally refuse to acknowledge that we know: "If Rumsfeld thinks that the main dangers in the confrontation with Iraq were the "unknown unknowns", that is, the threats from Saddam whose nature we cannot even suspect, then the Abu Ghraib scandal shows that the main dangers lie in the "unknown knowns" – the disavowed beliefs, suppositions and obscene practices we pretend not to know about, even though they form the background of our public values."
In his 2007 book The Black Swan: The Impact of the Highly Improbable, Nassim Nicholas Taleb tells of a presentation on uncertainty he was requested to give to the United States Department of Defense shortly before Rumsfeld's speech. The core message of The Black Swan is that unknown unknowns are responsible for the greatest societal change.
Rumsfeld named his autobiography Known and Unknown: A Memoir.