Epistemic (the greek word for knowledge, or the roots of knowledge) Trust refers to the specific kind of trust required by someone to allow learning (particularly social learning, about "how we behave in these circumstances") to take place by one person from another person.
Epistemic trust is that particular trust in the value of social knowledge that a potential "teacher" may have to offer the potential learner
Epistemic trust is built on (or triggered by) the knowledge that the teacher has authentically connected and sympathetically understood the crucial things about me - not about people in general, but about me in particular: the sense that "you have noticed and understood what it is like to be me, here, now, in THIS predicament."
What this refers to, then, is the experience that a teacher (who is adopting the "Pedagogical Stance") has accurately Mentalized me. As a potential learner, it is the experience of the Contingencies in what I get from you, my potential teacher (or therapist), and the little cues (things like appropriate eye contact, tone of voice, etc, that we refer to as Ostensive communication) that signal to me that I can trust what you have to offer in terms of social knowledge. On the other hand, every time I get Non-contingent experiences from you, the chances of my opening to learning from you in this way diminish.
Below is a video clip of Prof Fonagy explaining this concept in 15 minutes, below that is an animated sequence of slides that we use to explain the concept of Epistemic Trust, and the difficulties in their Relationship to help that many young people have.
* The young person has an opportunity to learn about himself by finding his own mind represented in the mind of a trusted other. * BUT, this does not account for the kinds of internal working models of what "help" is like (which may prompt the young person to avoid it) * NOR the strong drives not to know (because knowing about oneself can be a painful process)... * SO, many young people act in many ways that act as a screen to keep help at bay. * Epistemic Trust is triggered when they meet someone who gives them an experience of being understood in their own terms, in the specifics of the here and now... * This is understood as an evolved mechanism for helping humans to take on complex social learning from safe sources... "When I saw in your eyes that you had accepted me, understood me, right here, right now, it was as if the door opened and I was interested in what you had to say..."