Known unknowns

During a press conference in 2002 a reporter questioned Donald Rumsfeld, the then US Secretary of Defence, about the presence of weapons of mass destruction in Iraq.

Rumsfeld’s response included the famous line:

“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; there are things we do not know we don’t know.”

Unknown unknowns are a major problem when one is seeking to understand and asses a situation. You don’t know the critical piece of information and you don’t know that you need to know it.

Nate Silver discusses this idea in The Signal and the Noise and seeks to clarify the terms use:

“The concept of the unknown unknown is sometimes misunderstood. It’s common to see the term employed in formulations like this, to refer to a fairly specific (but hard-to predict) threat:

Nigeria is a good bet for a crisis in the not-too-distant future—an unknown unknown that poses the most profound implications for US and global security [emphasis added].

This particular prophecy about the terrorist threat posed by Nigeria was rather prescient (it was written in 2006, three years before the Nigerian national Umar Farouk Abdulmutallab tried to detonate explosives hidden in his underwear while aboard a flight from Amsterdam to Detroit). However, it got the semantics wrong. Anytime you are able to enumerate a dangerous or unpredictable element, you are expressing a known unknown. To articulate what you don’t know is a mark of progress.

Few things, as we have found, fall squarely into the binary categories of the predictable and the unpredictable. Even if you don’t know to predict something with 100 percent certainty, you may be able to come up with an estimate or a forecast of the threat. It may be a sharp estimate or a crude one, an accurate forecast or an inaccurate one, a smart one or a dumb one.* But at least you are alert to the problem and you can usually get somewhere: we don’t know exactly how much of a terrorist threat Nigeria may pose to us, for instance, but it is probably a bigger threat than Luxembourg.”