The Four Siddhāntas are the four methods employed by the Buddha to cause living beings to achieve accomplishment of attaining Buddhahood, or they can be the four viewpoints of perceiving truth.

The characteristics of the “Worldly Siddhānta” (Shih-chieh Hsi-t’an) concern the basic theory of causality (Yin-yüan) in Buddhism, and differentiate what is real and what is unreal. What is unreal (provisional) refers to all things in this spatial-temporal world that arise through Dependent Origination (Ch., Yüanch’i; Skt., pratityasamutpāda), rendering the fact that all things lack substantial Being, and are illusory. The unreal is spoken of in terms of the five aggregates bearing their existence in name. Names are not substantial, and thus, the five aggregates are only illusory and provisional. What is real (Shih) refers to the body that is constituted by the five aggregates, which really exists. In short, the Worldly Siddhānta distinguishes between phenomenon and noumenon, between real and unreal, between good and bad, and between different levels of religious practice and achievement. The teaching suits those beings that are capable of understanding the doctrine of the Worldly Siddhānta.

The characteristic of the “Siddhānta for Each Person” (Ko-ko Wei-jen Hsi-t’an) concerns the wholesome factors of beings, namely, arousing previous wholesomeness of beings, and encouraging them to keep doing good deeds and practice for their future destinies.

In contradistinction to the “Siddhānta for Each Person” (which is related to the wholesomeness of living beings), the “Siddhānta of Counteraction” (Tui-chih Hsi-t’an) is to treat the unwholesomeness of living beings. Hence, the characteristic of this siddhānta concerns the evil side of beings, namely, how to destroy evil by means of wholesomeness. This teaching of the Siddhānta of Counteraction reveals the goal of religious practice.

The “Siddhānta of the Supreme Truth” (Ti-i-i Hsit’an) reveals the principle (as truth) (Ti-li) by means of applying the formula of the fourth Alternative, namely, “everything is neither real nor unreal”, which transcends affirmation or negation. Therefore, the characteristic of this siddhānta concerns leading living beings to realize the truth by disposing the fundamental nature of emptiness of all entities, and by negating all possible attachments to either unreal (provisional) or real, and either good or evil. The passage concerning the Four Siddhäntas is originally stated in the Mahāprajn͂āpāramitopadeśa (Ta-chih-tu Lun), T.25, 59b-61b.

For a brief explanation of the Four Siddhāntas, see also Hurvitz, Chih-i, p.313, note l. For a detailed discussion of the Four Siddhāntas in the Ta-chih-tu Lun, see Swanson, Foundations of T’ien-t’ai Philosophy, pp.23-30. (Vol. 2, Page 53)