Originally: a public record or case. A Zen paradox, question or episode from the past that defies logical explanation. Koans are sometimes thought of as Zen riddles, but this is not entirely accurate since most riddles are intended to be solved through reason. A student undertaking koan work is meant rather to exhaust the use of reason and conceptual understanding, finally making an intuitive leap (see kensho). Koans were originally recorded and used by the Rinzai school of Zen, but some teachers closer to the Sōtō school have also used koans.