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)

This is the last part in elaborating the Four Siddhāntas. By stressing that the Four Siddhāntas are expressed in the Lotus Sūtra, Chih-i legitimizes his own view concerning the Lotus Sūtra as the ultimate teaching of the Buddha embracing all types of the teaching. The passage is quoted by Chih-i from the “Chapter on Expedient Means” (Fang-pien-p’in) in order to prove that the meaning of the Four Siddhāntas can be drawn from it:

“[The Buddha] understands all actions of living beings, what they think in their deep minds, their habitual tendencies [they carry] from the past, their desires, their nature, the power of their exertions, and whether their faculties are acute or dull. [The Buddha] employs various causes and conditions, similes, parables, and other words and phrases, adapting whatever means that are suitable to expound his teaching.”

This passage is interpreted by Chih-i as:

” ‘Desire’ is the [mundane] pleasure and desire, which indicates the Worldly Siddhānta. ‘Nature’ refers to the nature of knowledge and wisdom, which indicates the Siddhānta for Each Person. The ‘power of exertions’ refers to the destruction of evil, which indicates the Siddhānta of Counteraction. ‘Acute or dull faculties’ refers to different realizations attained by two people [with either acute or dull faculties], which indicates the Siddhānta of the Supreme Truth.”
Chih-i associates the phrases “their desires” with the Worldly Siddhānta (for the teaching suits the desire of living beings), “their nature” with the Siddhānta for Each Person (for nature means the nature of knowledge and wisdom which denotes the wholesomeness this teaching is intended to produce), “the power of their exertions” with the Siddhānta of Counteraction (for power is meant to destroy evil, which is the intended result of this teaching), and “whether their faculties are acute or dull” with the Siddhānta of the Supreme Truth (for the teaching aims at enlightening living beings of different capacities).

Through such an interpretation that reveals the meaning of the Four Siddhāntas implied in the Lotus Sūtra, the validity of the Lotus Teaching is confirmed.

Chih-i’s intention of differentiating the teaching of the Buddha is for the sake of presenting it as a whole. This is to say that although there are various types of the teaching, all of them are unified under the One Buddha-vehicle that is expressed in the Lotus Sūtra. Therefore, the Lotus Sūtra functions to dissolve the relative teachings into the ultimate teaching. Chih-i affirms that all of the relative teachings of the Three Vehicles (śrāvaka, pratyekabuddha, and bodhisattva) contain the real intention of the Buddha in leading sentient beings to attain Buddhahood. This intention of the Buddha is the ultimate teaching of the One Buddha-vehicle. By this definition, all types of the teaching of the Buddha are subtle. The distinction between the relative and the ultimate is only made to coincide with living beings separated from conceiving the subtlety of the Buddha’s teaching. Chih-i asserts that the only purpose for the Buddha to employ the coarse device as the relative teaching is for the ultimate teaching. In this sense, all types of the teaching of the Buddha in the five periods that are analogized with the five flavors of dairy products (milk, cream, curdled milk, butter, and ghee) contain subtlety. In terms of revealing the Ultimate Truth, the teaching of the five flavors is not dissimilar to each other. Once the ultimate teaching (i.e., Lotus Sūtra) is presented, there is no more coarseness or relativity, but subtlety. (Vol. 2, Page 44-45)

The Four Siddhāntas that are conveyed in the light of the Four Noble Truths in the Tripiṭaka, Common, and Separate Teachings, are relative teachings. The ultimate teaching of the Four Siddhāntas refers to the Perfect Teaching. Chih-i’s explanation of the Four Siddhāntas in terms of relative and ultimate that are related to each of the Four Teachings is as follows:

1. The Buddha employs only the first three Siddhāntas (i.e., Worldly Siddhānta, Siddhānta for Each Person, and Siddhānta of
   Counteraction) to expound the Four Noble Truths that belong to the Tripiṭaka Teaching. Since this teaching concerns analysis and disintegration of dharmas (entities) in perceiving emptiness and is to prepare listeners with lower faculties to be able to eventually receive Mahāyāna Teaching, it is unskillful in terms of the way of perceiving emptiness, and is relative.
2. The Four Siddhāntas the Buddha employs to expound the Four Noble Truths that belong to the Common Teaching are skillful, for the teaching concerns embodying dharmas in perceiving emptiness. That is, dharmas are empty therein. However, truth is dichotomized into the Absolute Truth and the Worldly Truth: the former concerns emptiness, and the latter empirical existence. This teaching of duality is relative.
3. The Four Siddhāntas the Buddha employs to expound the Four Noble Truths that belong to the Separate Teaching are profound, for this doctrine concerns the Middle Way of transcending the truths of emptiness and existence. However, this Middle Way does not identify emptiness with existence, and is still relative.
4. The Four Siddhāntas the Buddha employs to expound the Four Noble Truths that belong to the Perfect Teaching are ultimate and subtle. This is because this doctrine concerns the Middle Way that identifies emptiness with existence. For Chih-i, such a way of perceiving reality as an integrated unity of both emptiness and provisional existence is perfect and is the ultimate teaching of the Buddha. (Vol. 2, Page 43-44)