'five teaching periods.' A division of the periods of the varying methods used by S/a^kyamuni to explain the dharma from the time he attained enlightenment until the time he entered nirvana. Though there are various theories regarding these five， all are generally derived from the original explanation propounded by Huikuan 慧观 in the fifth century. （A） Huikuan's explanation divides the teaching into gradual 渐 and sudden 顿， further dividing sudden into the following five: （1） the Distinct Teaching of the Three Vehicles （a^gama Sutras， etc.）; （2） the Three Vehicle Shared Teaching （Prajn~a^pa^ramita^ Su^tra s， etc.）; （3） the Restraining and Praising Teaching （Vimalaki^rti Sutra 维摩经， etc.）; （4） the Teaching of the Shared Intent （Avatam!saka-su^tra 华严经， etc.） and （5） the Eternal Teaching （Nirva^na-su^tra 涅槃经， etc.）. This is the classification of the "Nirva^na school." （B） In the Huayan teaching of Liuqiu 刘 the Avatam!saka-su^tra is called the "Sudden teaching" and the "gradual teaching" is divided into the following five: （1） The Teaching of Men and Gods; （2） The Teaching of the Existence of Form （the a^gamas and so forth， that accept the existence of discriminated forms）; （3） The Formless Teaching （prajn~a^pa^ramita^ teaching， etc.， that denies the real existence of form）; （4） The Teaching of Shared Intent （Lotus Sutra， etc.） and （5） The Eternal Teaching （Nirva^na Sutra etc.） （C） Zhiyi altered the above （B） somewhat. According to Tiantai 天台 teaching， the five periods are: （1） The Huayan period. After the Buddha's enlightenment， he expounded the Avatam!saka-su^tra for 21 days for bodhisattvas. This was a teaching for those of very sharp faculties， and according to this teaching such bodhisattvas may directly awaken to the reality-principle. （2） The Deer Park period. After delivering the Avatam!saka-su^tra， ordinary people of undeveloped faculties are not able to understand， so he discards this teaching in favor of guiding people through expedient teachings. Thus he delivered the lesser vehicle teachings at Deer Park near Benares. This period was twelve years， and the scriptures that developed from this are the a^gamas， so it is also called the "a^gama period." （3） The Vaipulya period （Elementary Maha^ya^na）. For the people that had grasped the Hi^naya^na teachings， the Buddha now teaches Maha^ya^na Sutras such as the Vimalaki^rti Sutra， the Su^tra of the Golden Light and the Srimala Su^tra 胜鬘经， broadly explaining the Tripitaka， Shared， Distinct and Perfect Teachings. This is intended to convert people from Hi^naya^na to Maha^ya^na. This period lasts for eight years. （4） Perfection of Wisdom. For 22 years the Buddha teaches the Prajn~a^pa^ramita^ sutras in order to awaken people to the principle of emptiness. （5） The Lotus and Nirva^na period. The Buddha makes clear that the final goal of Hi^naya^na and Maha^ya^na is to same. Thus it is also called the Teaching of the Single Vehicle， wherein the presence of Buddha-nature in each person is affirmed.