In 2003, ex-sailor and then Secretary of Defense Donald Rumsfeld, said the following:
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.
Many in the mainstream press chuckled warmly upon hearing this. “What a typical, right-wing dolt!” they thought to themselves. Some said so out loud. For a brief while, it was enough to induce a laugh among our betters to merely say, “Unknown unknowns.” It might still work. Try it.
Civilian reporter Hart Seely was so tickled that he arranged Rumsfeld’s words in the form of verse. He did so because he thought that the words resembled “jazzy, impromptu riffs.”
Luckily, Mr Seely was known as a “humorist”, so his readers knew that they should laugh. And so they did. (Read a sample of verbal chuckles accompanying this YouTube video.)
However, not only was Mr Rumsfeld right in what he said, he expressed what he said beautifully and concisely. Worse news for our cultural guardians, it turns out that Rumsfeld was echoing the sainted John Maynard Keynes.
In 1937, Keynes said:
By ‘uncertain’ knowledge I do not mean merely to distinguish what is known for certain from what is only probable…The sense in which I am using the term is that in which the prospect of a European war is uncertain, or the price of copper and the rate of interest twenty years hence, or the obsolescence of invention, or the position of private wealth owners in the social system in 1970. About these matters there is no scientific basis on which to form any calculable probability whatever. We simply do not know.
This is from his shockingly neglected Treatise on Probability. For Keynes, probability was a branch of logic. He divided statements into three rough, overlapping categories. Statements which could have quantitative probability assessed, those that were only comparative, and those which are impossible to quantify.
An example of the first kind, well known to regular readers. Premise: We have a six-sided object, just one side of which is labeled “6”, which will be tossed once; only one side can show. Given that premise, the probability of the statement, “A ‘6’ will show” is 1 in 6.
An example of the first kind with data. Premise: the data of age of death and select biological characteristics for a large group of people. Given that premise (data can be a premise), and another about how that data is modeled, the probability of statements like, “John Smith will die aged 70 or older” can be computed to reasonable degree. These probabilities allow insurance agents to accost you.
A comparative example. Premise: From a bag in which there are more of A than B, one item will be drawn. Given that premise, we can do no better than to say that drawing an A is more likely than drawing a B. Many examples with vague data will suggest themselves.
A Rumsfeldian example of unknown unknowns. Before the fauna of Australia was well known, the swan was often used to illustrate logical arguments. Premise: All swans are white; Art is a swan. The conclusion, “Art is white” logically follows (it has probability 1).
While the European discovery of the black swan in no way invalidates the “white swan” argument, because the premise is assumed true, finding that all swans were not white was a bit of a shock. Nobody expected it. The surprise was such that philosophers dropped swans from their menagerie and switched to the humanity of Socrates for their stock example.
Nicolas Taleb used this example in his popular book. He, too cautions that people are too sure of themselves and that many events remain unpredictable (though he at least intimates that he has developed an investment system that is more immune to uncertainty than systems offered by others).
Of the three Keynesian categories, I believe it is the third which is the largest. That is, it is the unknown unknowns that outnumber all other kinds of knowledge. I cannot prove this: there can obviously be no proof. But all experience, and evidence that the universe is vast and ancient, suggests it is so.
Explicit acknowledgment of this was given by Harold Macmillan when he was asked what was most likely to blow governments off course. “Events, dear boy. Events.” This is no different than saying, “Unknown unknowns, dear boy.”
Looking into the future is exactly like peering through a thick fog. You can see what is right next to you with great detail. Items a little further off lose detail, while those beyond are completely opaque. And what you can see is different from what your neighbor can see.