The four teachings … are the methods of conversion that are like medical prescriptions for the world. …

1. THE SUDDEN METHOD

When the Buddha attained perfect complete awakening, he taught the Flower Garland Sūtra of the Mahāyāna teachings. According to its category and period, this sūtra reveals the sudden method of teaching. Other sūtra classification systems before and since Zhiyi treat “sudden” as a doctrinal category, rather than as a method of presenting doctrine. This sudden type of doctrine differs from the sudden method in that the doctrine itself can result in sudden awakening without the Buddha providing his listeners with preparatory knowledge.

2. THE GRADUAL METHOD

Because of the nature of the capacities of the listening disciples, the gradual method of preaching leads from the shallow teaching of Hinayāna to the deep teaching of Mahāyāna. This gradual method was used during the period of the Deer Park, the period of the Expanded teachings, and the period of the Perfection of Wisdom. The gradual method is also divided into three periods. The initial portion of the gradual method is the period of the Deer Park, when the teaching of Hinayāna was expounded in the Agama sūtras to guide the disciples and other people of lesser capacities. The middle portion of the gradual method is the period of the Expanded teaching, when the teachings of Hinayāna and Mahāyāna were mixed, and the Buddha admonished his disciples who were still following Hinayāna teachings in order to lead them to aspire for the Mahāyāna. The final portion of the gradual method is the period of the Perfection of Wisdom when only the teaching of Mahāyāna was expounded, and the Buddha taught the emptiness of the dharmas and that the separation between Hinayāna and Mahāyāna is illusory. Thus, the Buddha reveals his teachings in a specific order, according to people’s capacities.

3. THE SECRET METHOD

The secret method is indeterminate but hidden. Listeners hear the same teaching, but each understands it according to his or her respective capacity. Each therefore receives a different benefit from the teaching, without realizing that there is a difference between their understanding and that of other listeners.

4. THE INDETERMINATE METHOD

The indeterminate method is manifest and not hidden. Listeners hear the same teaching, but according to their capacities some take Mahāyāna as Hinayāna, while others take Hinayāna as Mahāyāna. Not only do they understand and benefit differently but they are aware of the difference.

These are the preaching methods of the four early periods of Flower Garland, Deer Park, Expanded, and Wisdom. However, the period of the Lotus and the Nirvāṇa Sūtras is not included in the four methods of teaching. That period transcends this classification system.