Kung-ans occurred very early in Ch'an history and simply become records of incidents between masters and disciples in the context of practice. These kung-ans were very much alive, spontaneous. Around the Sung Dynasty (960-1279) Ch'an masters began using kung-ans from the records as a method of meditation for their disciples. The practitioner was required to investigate the meaning of the historical kung-an. In his attempt to plumb the meaning of the kung-an, the student has to abandon knowledge, experience, and reasoning, since the answer is not suspectable to these methods. He must find the answer by ts'an kung-an 參公案, by "investigating the kung-an." This requires his sweeping from his consciousness everything but the kung-an. When there is nothing in his mind but the kung-an, there is a chance for an experience of Ch'an, an awakening.

Closely related, but not identical to the kung-an, is the hua-t'ou 話頭. A hua-t'ou, literally "head of a thought", is a question that the meditator inwardly asks himself. For example, "What is wu?", or "Who am I?". As in the kung-an, the answer is not resolvable through reasoning, but requires ts'an hua-t'ou 參話頭, "investigating the hua-t'ou." The meditator devotes his full attention to repeatedly, incessantly, asking himself the hua-t'ou. His objective is to probe into the source of the question, that is, the state of mind that existed before the question became a thought.

There are similarities between the kung-an and hua-t'ou. Both are methods of ts'an Ch'an, investigating Ch'an. In the sutras there was usually a dialogue between the Buddha and his disciples. The Buddha used this question-and-answer format to arouse the understanding of the disciples. The word ts'an is thus also applicable to the method of the Buddha.