By Schubert Ogden
...
2. X's de facto epistemic authority for Y is a grounded epistemic authority if, and only if, it is possible for someone – -- if not Y, then others – -- to test X's claims to knowledge in realm R. This means (1) that knowledge of what X claims to know can be attained otherwise than by relying on some epistemic authority; and (2) that there is an independent criterion by which all claims to knowledge in R can be tested.
...