Donald Rumsfeld is famous for his “unknown unknowns” quote. He has been much mocked for it. Normally, the last thing I would want to do is defend him, but I think this particular criticism of him is harsh. The full quote is:
“… 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.”
It comes from a 2002 briefing when he was questioned about the lack of evidence for weapons of mass destruction in Iraq. Incidentally the Wikipedia page has fascinating discussion of this quote.
His logic seems sound to me, and it applies to scientific research. Scientists can only observe and measure what our technologies allow us to. So we can split natural phenomena into three categories, like those of Rumsfeld.
The first is the “known knowns”, the things we are aware of and can measure reliably. The second is the “known unknowns”, the things we are aware of but cannot reliably measure. And the third is the “unknown unknowns”, things that we are not even aware of, and cannot measure.
Over the years and centuries, science has progressed, moving things from the “unknown unknowns” category to the “known unknowns”, and then to the “known knowns”. The planet Neptune is a classic example. Up until the nineteenth century it was an “unknown unknown”. We didn’t have a clue it was there. Then the orbit of the next planet in, Uranus, was measured and it did not fit the theory — something was up. Then Neptune became a “known unknown”. It was observed shortly afterwards, at which point its orbit at least entered the “known known” category.
I guess the moral here, is that when you are finding understanding elusive, it could be one of Rumsfeld’s unknown unknowns that you are missing.