Full Idea
Any non-trivial extension of a belief system is less probable than the original system, but there are extensions that are more coherent than the original system. Hence more coherence does not imply a higher probability.
Gist of Idea
Extending a system makes it less probable, so extending coherence can't make it more probable
Source
Erik J. Olsson (Against Coherence [2005], 6.4)
Book Reference
Olsson,Erik J.: 'Against Coherence' [OUP 2008], p.105
A Reaction
[Olson cites Klein and Warfield 1994; compressed] The example rightly says the extension could have high internal coherence, but not whether the extension is coherent with the system being extended.