A gong an is a story of an incident between a master and one or more disciples that involves an understanding or experience of the enlightened mind. The incident usually, but not always, involves dialogue. When the incident is remembered and recorded, it becomes a "public case, " which is the literal meaning of the term. Often what makes the incident worth recording is that, as the result of the interchange, a disciple had an awakening, an experience of enlightenment.

Master Zhaozhou was asked by a monk, "Does a dog have Buddha-nature?" The master replied, "Wu, " meaning nothing. This is a basic gong an, possibly the most famous on record. Here is another gong an, also involving Zhaozhou. Zhaozhou had a disciple who met an old woman and asked her, "How do I get to Mt. Tai?" She said, "Just keep going!" As the monk started off, he heard the old woman remark, "He really went!" Afterward, the disciple mentioned this to Zhaozhou, who said, "I think I will go over there and see for myself." When he met the old woman, Zhaozhou asked the same question and she gave the same response: "Just keep going!" As Zhaozhou started off, he heard the old lady said as she had last time, "He really went!" When Zhaozhou returned, he said to the assembly, "I have seen through that old woman!" What did Zhaozhou find out about that old woman? What is the meaning of this lengthy and obscure gong an?