- 0th Order - Lack of Ignorance (a known known)
- 1st Order - Lack of Knowledge (a known unknown)
- 2nd Order - Lack of Awareness (unknown unknowns)
- 3rd Order - Lack of Process (a lack of means of finding out that you don’t know that you don’t know)
- 4th Order - Meta ignorance (when you don’t know about the 5 orders of ignorance)
Bookmark of 'The Five Orders of Ignorance | October 2000 | Communications of the ACM'
From 0th (known knowns) to 4th (meta ignorance) - a gem from 2000