US Secretary of Defense has received general derision for the following rather convoluted statement
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
As I’m giving two papers on this general topic in the next couple of days, I feel I should come to his defense on this. Although the language may be tortured, the basic point is both valid and important.
The standard planning procedures recommended in decision theory begin with the assumption that the decisionmaker has foreseen every relevant contingency. Given this assumption, making the right decision is a simple matter of attaching probabilities (or, if you like my rank-dependent generalization of the standard model, decision weights) to each of the contingencies, attaching benefit numbers (utilities) to the contingent outcomes that will arise from a given course of action, then taking a weighted average. Whatever course of outcome yields the best average outcome is the right one to take. In this way, uncertainty about the future can be ‘domesticated’ and reduced to certainty equivalents.
The problem is that, in reality, you can’t foresee all possible contingencies = the ‘unknown unknowns’ Rumsfeld is talking about are precisely these unforeseen contingencies. Some of the time this doesn’t matter. If the unforeseen contingencies tend to cancel each other out, then the course of action recommended by standard decision theory will usually be a pretty good one. But in many contexts, surprises are almost certain to be unpleasant. In such contexts, it’s wise to avoid actions that are optimal for the contingencies under consideration, but are likely to be derailed by anything out of the ordinary. There’s a whole literature on robust decision theory that’s relevant here.
Having defended Rumsfeld, I’d point out that the considerations he refers to provide the case for being very cautious in going to war. Experience shows that decisions to go to war, taken on the basis of careful calculation of the foreseeable consequences, have turned out badly more often than not, and disastrously badly on many occasions. The calculations of the German military leading up to World War I, including the formulation of the Schleiffen plan, provide an ideal example.
Finally, I should mention that I saw a link at the time to a post somewhere that seemed, from the one sentence summary to be making a similar point, but I was too busy too follow it, and can’t now locate it. Anyone who can find it for me gets a free mention in the update.
UpdateAt least one such post has come to my attention, at Language Log, along with a useful link to Sylvain Bromberger who has, it seems, written extensively on the theory of ignorance. I will be keen to chase this up.
John Quiggin 
Without necessarily disagreeing with your specifics John, we had a long chat about this one over at Back Pages, where I finally assumed for the sake of the argument that Rummy was honestly seeking to describe the full set, composed of: known-knowns + known-unknowns + unknown-unknowns. Leaving aside a lot of minor quibbles, just ask what’s missing from the complete set? It is, of course, the “unknown-knowns”. As the old saying goes, ‘where you stand depends on where you sit’. What to the public is an “unknown-unknown” may well be a “known-known” to the administration, and this is therefore, in the social round, an “unknown-known”. There are also things that, from a historical point of view, are “known-knowns”, but in the administration’s understanding, appear to be “unknown-unknowns”. In the social round, these therefore also add up to “unknown-knowns”. The “unknown-knowns” are thus the key. Obfuscation meets elision, right on the spot where the public interest lies!
Thanks for this, Chris – the discussion was useful and interesting.
The Guardian stuck up for Rumsfeld’s use of language in a leader on 3/12/03:
“This is indeed a complex, almost Kantian, thought. It needs a little concentration to follow it. Yet it is anything but foolish. It is also perfectly clear. It is expressed in admirably plain English, with not a word of jargon or gobbledygook in it. A Cambridge literary theorist, US Air Force war gamer or Treasury tax law draftsman would be sacked for producing such a useful thought so simply expressed in good Anglo-Saxon words. So let Rummy be. The Plain English Campaign should find itself a more deserving target for its misplaced mockery.”
http://www.guardian.co.uk/leaders/story/0,3604,1098422,00.html
Kantian discourse can lead to trouble.
THis may be the first recorded instance of Pr Q and Mark Steyn being in agreement. Rummy speaks the truth, not gobbledygook
In the logic of game theor matrices, the Rumsfeld classification has the following exclusive and exhaustive categories. I shall use the example of the climate events elaborate.
X-axis: Knowns:
Known Knowns: today’s weather here
Known Unknowns tomorrow’s weather here
Y-axis: Unknowns:
Unknown Knowns: today’s whether in communicado elsewhere
Unknown Unknowns: tomorrow’s weather should an asteroid hit
Rumsfeld left out option three, which is evidently logically equivalent to dealing with the Saudi owned Carlyle Group, but being in denial that this is sleeping with the enemy.
i had exactly the same thought: namely that what rumsfeld said was perfectly clear.
(then again, i often thought what humphrey appleby said made perfect sense even though everyone else was just laughing and had lost track halfway through the last sentence)
i have to agree with the guardian, that rumsfeld made a very astute point in plain english, and with all due respect, i could follow rummy more easily than John’s extrapolation…
actually, i think john characterizes it slightly wrong. he replaces known unknowns with contigencies.
a contigency is a known possible course of events, we just dont know whether it will happen or not.
a known unknown is simply a logical premise, say osama is still in afghanistan, of which we dont know the value, true or false.
although i guess if one applies this to decisionmaking alone, john’s characterisation is fair.
[…] The Known Unknowns Revisited: I’m afraid I don’t agree with Double Yellow. To me both Rumsfeld and Wong Kan Seng make perfect sense. Mr. Wong’s words, however, are nowhere in the league of Rumsfeld’s, which has been hailed as anything from valid and important to a useful thought so simply expressed in good Anglo-Saxon words. […]
[…] so influential. That these monumental events will emerge from the ‘unknown unknowns’, the principle famously articulated by Donald Rumsfeld at a press conference regarding events in Iraq in 2002, that it’s the things we don’t […]
[…] reception by the press was mixed: some accused him of playing with words with little meaning, while others saw some method in what he was trying to […]