Full Idea
A schizophrenic who thinks he is Napoleon, if he has a completely consistent story with enough interlocking details, may have a belief system that is superbly coherent.
Gist of Idea
A consistent madman could have a very coherent belief system
Source
Robert Audi (Epistemology: contemporary introduction [1998], VII p.194)
Book Reference
Audi,Robert: 'Epistemology: a contemporary introduction' [Routledge 1998], p.194
A Reaction
This is an exaggeration, but the fact is that one isolated lie is totally coherent, so coherence can only emerge when a system is large. Sense experience must be central to coherence.