Epistemology is the study of how we know what we know. If we take a concept like integrity, epistemology would ask: how do we know integrity when we experience it in ourselves or encounter it in others?
What do you think? When in your life have you known that you had integrity, or that integrity was part of who you are? When in your life have you known integrity in someone else? These are difficult questions.
It's easier to ask: who comes to mind when you think of integrity? Is it someone who has it or someone who lacks it?
I like to think of integrity as having the strength and flexibility to withstand external force and stay yourself. It means that sometimes you resist and sometimes you bend so that you can bounce back. It means that the main part of you stays the same no matter how your circumstances change.
It's hard to know yourself well enough to be sure that you are staying the same when strong external forces are pressuring you. It's hard to know that the "you" you are experiencing now is substantially the same as the "you" that existed a minute or a month or a decade ago. We value integrity not because it is easy to have or to know but because our brains are always occupied in giving us the impression that something in us stays the same while everything else changes.
Congruence is a concept in NLP that means that all your awareness is wrapped around just one thing. It means that mind and body, consciousness and unconscious process are part of just one self moving in just one direction. Congruence is not the same as integrity, but integrity is very difficult without it.
Without congruence, integrity depends on maintaining the tenuous relationship between the you that you know and the you that you don't know, that self that runs below the surface and offers you words and behaviours and choices. There could, arguably, be integrity in maintaining a separation or a tension between those two selves. But it is unlikely that it is a very human integrity.
When human beings are fighting themselves, they tend to change. The conscious mind and the unconscious awareness react differently to external pressures. One shifts more than the other, the balance is lost, the integrity fails. It is every bit as scary as it sounds. This is the state in which one surprises oneself, and the surprise is not good. This is the state when you find yourself capable of things you thought you would never say or never do.
Lasting integrity is not about being the self you choose to acknowledge: it is about acknowledging the whole of the self you are. It demands that the conscious self make peace with the unknowable within you, and that the unconscious self be respectful of the limits and role of consciousness. It means continually returning to a state of congruence, especially when external forces seem to be pushing you off track and out of sync with yourself.
You don't have to think about how to find that state of congruence. You know it. You do have to think about wanting it and owning it and living with who you are congruently. That's the sign that conscious and unconscious process are willing to work together. It's the intention to be all of one piece that allows you to find the you that withstands change, the you that has integrity.