Full Idea
To know the limits of knowledge, we would have to know both sides of the limit.
Gist of Idea
You can only know the limits of knowledge if you know the other side of the limit
Source
John Searle (The Rediscovery of the Mind [1992], Ch. 1.V.6)
Book Reference
Searle,John R.: 'The Rediscovery of the Mind' [MIT 1999], p.24