Around the time of the Song dynasty (960-1276), Ch'an masters began using recorded gong ans as a subject of meditation for their disciples. The practitioner was required to investigate the meaning of the historical gong an. To penetrate the meaning of the gong an, the student has to abandon knowledge, experience, and reasoning, since the answer is not accessible by these methods. The student must find the answer by can (pronounced: tsan) gong an, or "investigating the gong an." This requires sweeping from consciousness everything but the gong an, eventually generating the "doubt sensation, " which is a strong sensation of wonder and an intense desire to know the meaning of the gong an.

Closely related, but not identical to, the gong an is the huatou. A huatou ─ literally, "head of a spoken word" ─ is a question that a practitioner asks himself or herself. "What is Wu?" and "Who am I?" are commonly used huatous. In the huatou practice, one devotes one's full attention to repeating the question incessantly. The gong an and the huatou methods are similar in that the practitioner tries to arouse the great doubt sensation in order to eventually shatter it and awaken to enlightenment.