When I accept someone's testimony, I am thus only a small part of the full seat of epistemic competence, which might include many others in a long chain. My own contribution might then be slight, just through the perceptual and linguistic competence involved in knowing what someone is saying or writing, etc.

When there are conflicts of observation, when experiments cannot be replicated, scientists may then retreat to a study of the various specific observations so as to explain the conflict, in the course of which they would make use of the concept of observation, or of some specification of that concept.

If we have a better understanding of knowledge than we do of such justification or competence, then we can explain the latter through the former.

There's not much to be done about the impossibility. One must instead get rid of the desire.

Given its more substantial aim, a judgment is apt only if its constitutive alethic affirmation is not only apt but aptly apt. The subject must attain aptly not only the truth of his affirmation but also its aptness. And that in turn requires not only the proper operation of one's perception, memory, inference, etc., but also that one deploy such competences through competent epistemic risk assessment.

Through our perceptual systems, we represent our surroundings, aiming to do so accurately, where the aiming is functional or teleological, rather than intentional. And the same goes for our functional beliefs. Through our judgments, however, we do intentionally, even consciously, attempt to get it right.

When I accept someone's testimony, I am thus only a small part of the full seat of epistemic competence, which might include many others in a long chain. My own contribution might then be slight, just through the perceptual and linguistic competence involved in knowing what someone is saying or writing, etc.