A monastic rank, held by a person who has served as head seat (shuso 首座) for one retreat (kessei ango 結制安居) and gone through rite of dharma combat (hossen shiki 法戰式). Only monks who are fully fledged are qualified to assume an abbacy (jūshoku 住職). During the Edo period (1600-1868), a monk had to undergo a minimum of twenty years of monastic training after ordination before becoming fully fledged. At present, the minimum is five years. Ideally, a monk becomes fully fledged after serving as head seat for one retreat at a training monastery. Most trainee monks (unsui 雲水) today, however, do not remain at a monastery long enough to get a turn at being head seat, so they serve as head seat at an abbreviated retreat (ryaku kessei 略結制) instead. Abbreviated retreats may last only two days or a week, and are often held in conjunction with the installation of a new abbot (shinzan shiki 晉山式).