Literally "first," "chief," or "head" (shu 首) "seat" (za, so 座): the seat in a sangha hall (sōdō 僧堂) held by the monk deemed leader of the sangha hall assembly (sōdōshu 僧堂衆), also called the great assembly (daishu 大衆). An officer in a monastic bureaucracy; one of the six prefects (roku chōshu 六頭首). In Song dynasty Chinese and medieval Japanese Zen monasteries, the head seat was subordinate to the rector, who had overall responsibility for discipline in the sangha hall and occupied official quarters (ryō 寮) located nearby. The head seat resided in the sangha hall and served as leader of the great assembly that was based there. The head seat was not necessarily the member of the sangha hall assembly who had the most monastic seniority as measured by years since ordination: the position was usually held by a promising younger monk who was on track to someday become an abbot. It was also customary for a retired senior officer, who held a position known as rear hall head seat (godō shuso 後堂首座), to act as an advisor and assistant to the head seat. During each retreat there was a "dharma combat ceremony" (hossen shiki 法戰式), a convocation in the dharma hall at which the head seat took the place of the abbot and responded to questions from monks of the assembly. In the bureaucratic structure that took hold in medieval Japan, serving as head seat in a monastery for at least one retreat and being tested in a dharma combat ceremony became a prerequisite for promotion to an abbacy.
In contemporary Soto Zen, the position of head seat remains an important and prestigious one at training monasteries. Moreover, service as head seat for one retreat (kessei ango 結制安居), at which one goes through rite of dharma combat (hossen shiki 法戰式), remains a formal requirement for attaining the rank of a fully fledged (risshin 立身) monk, which in turn is a prerequisite for becoming the abbot (resident priest; jūshoku 住職) of a temple. The great majority of young men who undergo training at Soto monasteries are the sons of resident priests who are expected to succeed their fathers as the abbots of ordinary temples, so they all need to serve as head seat for at least one retreat. Because it is not possible for all of them to do so for a full ninety-day retreat at a training monastery, many serve as head seats at an abbreviated retreat (ryaku kessei 略結制) instead. Abbreviated retreats may last only a few days, and are often held in conjunction with the installation of a new abbot (shinzan shiki 晉山式). →"fully fledged," "six prefects."