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Rumsfeld during a Pentagon news briefing in February 2002 "There are unknown unknowns" is a phrase from a response United States Secretary of Defense Donald Rumsfeld gave to a question at a U.S. Department of Defense (DoD) news briefing on February 12, 2002, about the lack of evidence linking the government of Iraq with the supply of weapons of mass destruction to terrorist groups. [1]
A fixed model considers the "known unknowns", but ignores the "unknown unknowns", made famous by a statement of Donald Rumsfeld. [19] The term "unknown unknowns" appeared in a 1982 New Yorker article on the aerospace industry, which cites the example of metal fatigue, the cause of crashes in Comet airliners in the 1950s. [20]
Popular discussion of unknowability grew with the use of the phrase There are unknown unknowns by United States Secretary of Defense Donald Rumsfeld at a news briefing on February 12, 2002. In addition to unknown unknowns there are known unknowns and unknown knowns. These category labels appeared in discussion of identification of chemical ...
Uncertainty is sometimes classified into two categories, [8] [9] prominently seen in medical applications. [10]Aleatoric Aleatoric uncertainty is also known as stochastic uncertainty, and is representative of unknowns that differ each time we run the same experiment.
If, on the other hand, the ranks of these two matrices are equal, the system must have at least one solution; since in an underdetermined system this rank is necessarily less than the number of unknowns, there are indeed an infinitude of solutions, with the general solution having k free parameters where k is the difference between the number ...
For example, if it is unknown whether or not it will rain tomorrow, then there is a state of uncertainty. If probabilities are applied to the possible outcomes using weather forecasts or even just a calibrated probability assessment, the uncertainty has been quantified. Suppose it is quantified as a 90% chance of sunshine.
A variable may denote an unknown number that has to be determined; in which case, it is called an unknown; for example, in the quadratic equation ax 2 + bx + c = 0, the variables a, b, c are parameters, and x is the unknown. Sometimes the same symbol can be used to denote both a variable and a constant, that is a well defined mathematical object.
Hence, the statement "p is an unknown truth" cannot be both known and true at the same time. Therefore, if all truths are knowable, the set of "all truths" must not include any of the form "something is an unknown truth"; thus there must be no unknown truths, and thus all truths must be known. This can be formalised with modal logic.