Koans and hua-t'ous are both methods of ts'an Ch'an, "investigating Ch'an." Because the Buddha sometimes used a question-and-answer format to deepen the understanding of his disciples, the word ts'an is also applicable to the Buddha's teaching methods. Another instance of ts'an Ch'an is the practice of making the rounds to accomplished masters in order to engage them in dialogue. Sometimes the practitioner has reached an impasse in his investigation, and he needs some "turning words" from a master to give him the impetus for a breakthrough. Advanced practitioners also visited masters in order to assess their own understanding of Ch'an or certify their own attainment. Koans and hua-t'ous were well-suited to these situations. Any interchange between master and disciple can be an opportunity for a live, spontaneous koan or hua-t'ou; these practices are not limited to sayings and questions from the historical record.

Another way in which koans and hua-t'ous are related is that a hua-t'ou can give rise to a koan, and vice versa. For example, the question "lf all the myriad things in the universe return to the One, to what does the One return?" was originally a hua-t'ou. When a student asked Master Chao-chou this same question, he answered, "When I was in Ch'ing Province I had one hempen shirt made weighing seven pounds." This exchange became an important koan. Conversely, a key phrase in a koan frequently serves as the source for a hua-t'ou. Thus "What is Mu?" is derived from the koan "Does a dog have Buddha-nature?"