Full Idea
The 'warrant' for a belief is that, whatever it is, that makes the difference between mere true belief and knowledge.
Gist of Idea
The 'warrant' for a belief is what turns a true belief into knowledge
Source
Trenton Merricks (Objects and Persons [2003], §7.II)
Book Reference
Merricks,Trenton: 'Objects and Persons' [OUP 2003], p.173
A Reaction
Hence a false belief could be well justified, but it could never be warranted. This makes warrant something like the externalist view of justification, a good supporting situation for a belief, rather than an inner awareness of support for it.