Koan (n.) literally means "public document," a case that sets a legal precedent — Zen's ingenious way to test insight and to pass it on with minimal falsification.
Koan (n.) hides its point by making it far more obvious than one would expect.
Koan (n.) was too artificial for the Soto school: it invites the very seeking that pushes satori away, or worse, induces a fake one.
Koan (n.) dropped into a clear mind is like a pebble tossed in a pool; the student simply watches what his mind does with it.
Koan (n.) is a hidden form of the student's own question: "Who wants to be liberated? Show me this you!"
Koan (n.) puts the student in an extreme double bind: show your naked self before supreme authority, be spontaneous on purpose, concentrate without thinking — and never comment.
Koan (n.) of Nansen's cat froze his monks when he demanded a true word — while Joshu, told of it later, simply put his sandals on his head and walked out.
The Koan (n.) has no symbolic meaning and is about nothing, yet it is something: that obvious, much-ignored thing called life.
The Koan (n.) catches every answer: say yes and you assert, say no and you deny — the tail is still in the gate.
The Koan (n.) is a problem-question built to drop the Zen student straight into a double bind.