The Dharma spoken by the Buddhas was divided into five periods and eight teachings by the Great Master Zhi Yi, "The Wise One" (538-597 A.D.). The five periods will be categorized by means of the two kinds of wisdom, expedient and actual.

1) The Avatamsaka period represented in the world by the Avatamsaka Sutra, consists in the Dharma spoken by the Buddha during the first twenty-one days of his teaching. The period includes one kind of expedient Dharma and one kind of actual Dharma: the gradual and the sudden. That is, the Avatamsaka Sutra teaches one kind of expedient wisdom and one kind of actual wisdom. The Avatamsaka Sutra explains the doctrine of the dharma realms: the dharma realm of phenomena; the noumenal dharma realm; the dharma realm in which phenomena are unobstructed; the dharma realm in which noumenon is unobstructed; and the dharma realm in which both phenomena and noumenon are unobstructed. Although this teaching was spoken for the sake of Bodhisattvas, the Avatamsaka Sutra nonetheless contains one kind of expedient dharma, along with the actual wisdom, that is, along with the real Buddhadharma.

2) In the second or Agama period, the Buddha spoke no actual Dharma, or actual wisdom, but instead spoke an expedient Dharma. At that time all sentient beings were like children, and since they did not understand the Buddhadharma, the Buddha used various expedient dharma-doors to induce and guide them, to transform them, and to take them across.

3) During the third period, the Vaipulya, the Buddha spoke three kinds of expedient Dharma and one kind of actual Dharma. At that time the four teachings were explained together: the treasury (tripitaka) teaching of the Hinayana; the connecting teaching; and the special teaching, which are the three expedient dharmas; and the perfect teaching, which is actual Dharma. "Revile the one-sided and upbraid the small" indicates that the one-sidedness of the small vehicle, the Hinayana, is wrong. "Praise the great and extol the perfect" commends the perfect teaching of the great vehicle, the Mahayana. In the Vaipulya period, the four teachings were explained together.

4) The fourth period is the Prajna period. In it there were two kinds of expedient Dharma – the connecting and special teachings – and one kind of actual Dharma, the perfect teaching.

5) In the Lotus-Nirvana period, which includes the Wonderful Dharma Lotus Flower Sutra and the Mahaparinirvana Sutra, there was no expedient Dharma; there was only actual Dharma and actual wisdom.

To summarize the five periods, in the Lotus-Nirvana period, only actual Dharma appears; there is no expedient Dharma. In the Prajna period, two expedient dharmas and one actual Dharma appear. In the Vaipulya period, three expedients and one actual Dharma appear. In the Agama period there is only expedient and no actual Dharma, and in the Avatamsaka period there is one expedient and one actual – the gradual and the sudden. The above explanation employs the two types of wisdom, expedient and actual, to categorize the five periods. If the periods were explained in detail, there would be much, much more to say.

So in lecturing on the sutras I explain a little more each time, I tell you a little more of what you haven't heard. Listen a lot and you will understand a lot.