"There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know."
- "There are known knowns." Here Rumsfeld seems to be talking about what philosophers call the "KK principle." That is, if p is known, then it is known that p is known. (Although Rumsfeld is not saying that every known is also a known known.) But what does it take to know that one knows that p? Presumably, the justification for knowing that p cannot be the same as the justification for p. So what could justify knowing that p?
- "There are known unknowns." Here Rumsfeld seems to to be talking about ordinary doubt. That is, in some cases we have doubts about whether or not we really know that p, and so we know that we don't know that p. In such cases, the grounds for doubt can be eliminated or cleared up. For example, suppose that while taking an exam I come across a question that stumps me. I don't know the answer to the question and I know that I don't know the answer to the question, since I skipped the material that this question is about while studying for the exam. In principle, however, any doubts I have about the right answer to this question can be eliminated or cleared up by consulting the relevant material or asking the professor after the exam.
- "there are also unknown unknowns." Here Rumsfeld seems to be talking about skepticism, not simply ordinary doubt. Skeptical scenarios, such as The Matrix and Inception, are supposed to show that most of our beliefs are in this category of "unknown unknowns." For, if we cannot rule out these skeptical possibilities, the skeptic argues, then our beliefs (e.g., "I am eating a steak") would not amount to knowledge. But why do we have to be able to rule out skeptical possibles in order to claim to know that p? Do you accept the skeptic's premise that, if Cypher is not justified in believing that he is not in The Matrix, then his belief that he is eating a steak fails to be knowledge?