Number four is extremely important in Chih-i’s system of classification. The well-established Buddhist notions, such as the Four Noble Truths and the Twelvefold Causality are corresponded by Chih-i’s own theory of the Four Teachings. Coherently, his theories of the four types of the Four Noble Truths and the four types of the Twelvefold Causality are formulated corresponding to the Four Teachings. In my opinion, the number four that is embodied by the Four Teachings is consciously or unconsciously significant to Chih-i. Number four represents the four seasons of a year, signifying a complete cycle of succession. With different seasons, different kinds of plants are able to grow. Our understanding of Chih-i’s use of number four is that, like the function of all four seasons which allow all plants to grow and to ripen, the Fourfold Teaching is designed by Chih-i to signify that it addresses all sentient beings with different capacities. (Pages 126-127)