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"There are known knowns" are the best known words of a verbal answer to a question at a US Department of Defense News Briefing made by Donald Rumsfeld while serving as United States Secretary of Defense in February 2002.
|“||... there are known knowns; 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.
The above statement was made by Rumsfeld on February 12, 2002 at a press briefing where he addressed the absence of evidence linking the government of Iraq with the supply of weapons of mass destruction to terrorist groups. It was criticised as an abuse of language by, among others, the Plain English Campaign. However, linguist Geoffrey Pullum disagreed, saying the quotation was "completely straightforward" and "impeccable, syntactically, semantically, logically, and rhetorically".
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."
|“||A subject is certain of something when he knows that thing; he is uncertain when he does not know it, but he knows he does not: he is consciously uncertain. On the other hand, he is unaware of something when he does not know it, and he does not know he does not know [emphasis added], and so on ad infinitum: he does not perceive, does not have in mind, the object of knowledge. The opposite of unawareness is awareness.||”|
|“||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.||”|
Žižek also builds the ideas of known unknowns, and unknown knowns, into a lecture on The Reality of the Virtual and a lecture on Architecture and aesthetics.
The term unknown unknowns was in use within the United States aerospace and military communities long before Rumsfeld's quote to the press in 2002. As early as 1969, Fortune magazine ran an article highlighting 'Unk-Unk' as an abbreviation used at Lockheed for 'unknown unknown'. An earlier use of the term in a military context comes from a 1984 paper about warfare:
|“||To those things Clausewitz wrote about uncertainty and chance, I would add a few comments on unknown unknowns – those things that a commander doesn't even know he doesn't know. Participants in a war game would describe an unknown unknown as unfair, beyond the ground rules of the game. But real war does not follow ground rules, and I would urge that games be "unfair" by introducing unknown unknowns.||”|
Around the same time, libertarian lawyer Richard Epstein wrote a well known article in the University of Chicago Law Review about the American labor law doctrine of employment at will (the idea that workers can be fired without warning or reason, unless their contract states otherwise). In giving some of his reasons in defense of the contract at will, he wrote this:
|“||The contract at will is also a sensible private adaptation to the problem of imperfect information over time. In sharp contrast to the purchase of standard goods, an inspection of the job before acceptance is far less likely to guarantee its quality thereafter. The future is not clearly known. More important, employees, like employers, know what they do not know. They are not faced with a bolt from the blue, with an "unknown unknown". Rather they face a known unknown for which they can plan. The at-will contract is an essential part of that planning because it allows both sides to take a wait-and-see attitude to their relationship so that new and more accurate choices can be made on the strength of improved information.||”|
The expression was used more recently, in 2005, in the context of risk and reliability:
|“||NASA space exploration should largely address a problem class in reliability and risk management stemming primarily from human error, system risk and multi-objective trade-off analysis, by conducting research into system complexity, risk characterization and modeling, and system reasoning. In general, in every mission we can distinguish risk in three possible ways: a) known-known, b) known-unknown, and c) unknown-unknown. It is probable, almost certain, that space exploration will partially experience similar known or unknown risks embedded in the Apollo missions, Shuttle or Station unless something alters how NASA will perceive and manage safety and reliability.||”|
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 used the quote in the title of his autobiography Known and Unknown: A Memoir.
Since Rumsfeld's speech, the full quote and the terms "known knowns" and "unknown unknowns" have appeared in popular culture: