In 2002, referring to Iraq and its relationship to terrorism, Donald Rumsfeld declared "that there are known knowns, there are things we know we know. We also know that there are known-unknowns, that is to say we know there are some things that we do not know, but there are also unknown-unknowns – the ones that we don't know we don't know."
Michael J. Graetz,
The Known Unknowns of the Business Tax Reforms Proposed in the House Republican Blueprint,
Colum. J. Tax L.
Available at: https://scholarship.law.columbia.edu/faculty_scholarship/2240