Full Idea
A justified belief that a proposition is not true is an 'overriding' defeater, ...and the belief that a justification is inadequate or defective is an 'undermining' defeater.
Gist of Idea
'Overriding' defeaters rule it out, and 'undermining' defeaters weaken in
Source
Albert Casullo (A Priori Knowledge [2002], n 40)
Book Reference
'Oxford Handbook of Epistemology', ed/tr. Moser, Paul K. [OUP 2002], p.140
A Reaction
Sounds more like a sliding scale than a binary option. Quite useful, though.