Buddhist epistemology (acknowledging that saying “epistemology” risk applying a philosophical concept to Buddhism that doesn’t totally make sense within Buddhism) makes a distinction between “form” and “emptiness”. To a first approximation, this is the same distinction rationalists point at with “map” and “territory”, respectively, but the map/territory metaphor sets up a particular type of correspondence relationship that is not inherent in the form/emptiness relationship because, as it says in the Heart Sutra, form is emptiness and emptiness is form, meaning that from and emptiness are with each other and cannot be isolated from one another (other than conceptually). Put another way, the map exists in the territory, and the territory is known because it is mapped.
The ground truth is just what is. And what is is mind, or experience, and the world that we know is nothing more than that experience. We then draw many inferences about this world and contingently come to believe them like “things exist independent of my experience of them” and “things will go on after I die” that result in having a conventional understanding of the world as an external reality, but in fact that sense of an external reality is justified only by knowledge gained from experience, so experience is what is fundamental, not reality (the inverse of this, saying that reality is fundamental and then we experience it, is to make a metaphysical assumption, though I want to note that even conceptualizing experience as experience also makes a kind of metaphysical assumption and the true dharma is completely wordless and thoughtless for this reason).
So, when we look at a koan, the ground truth it is trying to get us to see is this kind of thing, where we totally blow through even the smallest hint of ontology or thinking and just see what is within our field of experience.
Everything else is layers of trying to make sense of that experience and trying to help students get access to it and know if they really have access to it, since the mind is happy to play tricks on us and say “oh yeah this is direct experience” when in fact there were unseen layers of ontology. We rely on teachers to help us verify if our experience of experience is direct because others are better at spotting our blind spots than we are, but there is a fundamental uncertainty here that to be clear cannot be resolved because all knowledge is fundamentally uncertain (this is, incidentally, why I’m writing a book with the same title!).
Hopefully that answers several of your questions!
To look at the matter from yet another angle: how did these practices originate? Someone who first considers a koan which heretofore has not been considered by anyone, has no teacher who can verify his understanding. How do we get from that, to a state of affairs where the koan’s true understanding is known, and can be verified?
How did the koans first get written, and how did the people who wrote them know that they had understood them properly?
Koans are public cases. They were originally just teaching stories passed down as part of an oral tradition. Several centuries later they were written down in collections. It’s not clear exact when the type of koan practice we’ve been talking about started, but it happened sometime between 950 and 1250 CE in China because the founders of Zen in Japan who brought Chan Buddhism from China and refined a version of koan practice. Koan practice then later mostly disappeared in the Soto school and became formalized in the Rinzai school. Almost all koan practice we’ve been talking about here was passed down to us via the Rinzai tradition, although in America since the 1960s there’s been a revitalization of koan practice that has sought to move away from the formality of specific correct “answers” and towards more intuitive understanding.
We don’t really know the details of how koan practice got started. We can infer that one or more teachers developed the practice iteratively as a teaching aid to help their students realize the dharma. Koans sometimes contain proto-koans within them, and they give us a clue to koans being an attempt to give structure to an older tradition of “wild” behavior that showed that someone could wholehearted act outside the expectations of social norms, meaning an ability to return to lost access to natural, unsocialized behavior that we all have when we are very young but then quickly lose. This kind of wild Zen behavior continues to exist today, but it always and everywhere stamped down unless it is judged to be genuine to prevent imitation.
Buddhist epistemology (acknowledging that saying “epistemology” risk applying a philosophical concept to Buddhism that doesn’t totally make sense within Buddhism) makes a distinction between “form” and “emptiness”. To a first approximation, this is the same distinction rationalists point at with “map” and “territory”, respectively, but the map/territory metaphor sets up a particular type of correspondence relationship that is not inherent in the form/emptiness relationship because, as it says in the Heart Sutra, form is emptiness and emptiness is form, meaning that from and emptiness are with each other and cannot be isolated from one another (other than conceptually). Put another way, the map exists in the territory, and the territory is known because it is mapped.
The ground truth is just what is. And what is is mind, or experience, and the world that we know is nothing more than that experience. We then draw many inferences about this world and contingently come to believe them like “things exist independent of my experience of them” and “things will go on after I die” that result in having a conventional understanding of the world as an external reality, but in fact that sense of an external reality is justified only by knowledge gained from experience, so experience is what is fundamental, not reality (the inverse of this, saying that reality is fundamental and then we experience it, is to make a metaphysical assumption, though I want to note that even conceptualizing experience as experience also makes a kind of metaphysical assumption and the true dharma is completely wordless and thoughtless for this reason).
So, when we look at a koan, the ground truth it is trying to get us to see is this kind of thing, where we totally blow through even the smallest hint of ontology or thinking and just see what is within our field of experience.
Everything else is layers of trying to make sense of that experience and trying to help students get access to it and know if they really have access to it, since the mind is happy to play tricks on us and say “oh yeah this is direct experience” when in fact there were unseen layers of ontology. We rely on teachers to help us verify if our experience of experience is direct because others are better at spotting our blind spots than we are, but there is a fundamental uncertainty here that to be clear cannot be resolved because all knowledge is fundamentally uncertain (this is, incidentally, why I’m writing a book with the same title!).
Hopefully that answers several of your questions!
Koans are public cases. They were originally just teaching stories passed down as part of an oral tradition. Several centuries later they were written down in collections. It’s not clear exact when the type of koan practice we’ve been talking about started, but it happened sometime between 950 and 1250 CE in China because the founders of Zen in Japan who brought Chan Buddhism from China and refined a version of koan practice. Koan practice then later mostly disappeared in the Soto school and became formalized in the Rinzai school. Almost all koan practice we’ve been talking about here was passed down to us via the Rinzai tradition, although in America since the 1960s there’s been a revitalization of koan practice that has sought to move away from the formality of specific correct “answers” and towards more intuitive understanding.
We don’t really know the details of how koan practice got started. We can infer that one or more teachers developed the practice iteratively as a teaching aid to help their students realize the dharma. Koans sometimes contain proto-koans within them, and they give us a clue to koans being an attempt to give structure to an older tradition of “wild” behavior that showed that someone could wholehearted act outside the expectations of social norms, meaning an ability to return to lost access to natural, unsocialized behavior that we all have when we are very young but then quickly lose. This kind of wild Zen behavior continues to exist today, but it always and everywhere stamped down unless it is judged to be genuine to prevent imitation.