Excerpt from "Beyond the Daode jing Twofold Mystery in Tang Daoism" by Friederike Assandri
Twofold Mystery (chongxuan 重玄) is a Daoist teaching that was popular in the early seventh century. Its most salient feature is the creative use of a technique of reasoning, which is based on the logic of the four propositions (tetra lemma, siju 四句), a series of four statements where each negates the previous one:
•All dharmas are being (you 有)
•All dharmas are nonbeing (wu無)
•All dharmas are being and nonbeing (yi you yi wu 亦有亦無)
•All dharmas are neither being nor nonbeing (fei you fei wu 非有非無)
The logic of the tetra lemma came from India, where it formed a conceptual tool intellectuals of all traditions used in debate. The foremost philosopher of the Buddhist Mādhyamika School or Teaching of the Middle Way, Nāgārjuna (2 nd c. C.E.), relied on this logic not only to refute his opponents but also to develop his teaching. He used it to guide adepts through a process of successive negations to realise the ultimate unity beyond all possible distinctions, thus to attain enlightenment.
His teaching counters the risk of nihilism or ethical relativism, inherent in a continuation of negation, by combining the logic of the tetra lemma with the theory of two levels of truth.This theory postulates that any statement about being (like “everything exists” or “everything is nonexistent”) has two different levels: worldly truth (shidi 世諦) and absolute truth (zhendi 真諦)—depending on the capacity and the spiritual state of any being. Enlightenment and salvation consist in realising ultimate reality as absolute truth. This could not be achieved without first passing through the stages of worldly truth, and it was on the level of worldly, or conventional, truth that ethics and teachings mattered. Both notions are exemplified in the tetra lemma, so that each step serves as a move toward final realisation of the absolute, forming a pedagogical device to overcome one‑sided conceptions and eventually realise ultimate truth. While ordinary people generally accept the statement “everything exists,” enlightened or spiritually advanced adepts find this a merely worldly truth and consider it not valid. Their truth is: “everything is nonexistent.” This is so because they have realised that everything exists only because of conditioned causation and thus does not have a “true existence.” Therefore, they understand that the nature of all being is empty. On this level, their truth can be called absolute truth. However, the progression does not stop here. The insight into the “nonexistence” of being may still be considered one‑sided and therefore just another variant of worldly truth. Someone on a yet higher level of spiritual realisation may realise that everything is existing and nonexisting at the same time. This realisation again constitutes absolute truth. Nevertheless, even this new realisation can be overcome and thus becomes yet again a form of worldly truth. The absolute truth of even more advanced spiritual beings is the realisation that everything is neither existing nor not existing. This absolute truth cannot be refuted by further negation. It constitutes a realisation of the ultimate, which is interpreted as enlightenment or, in Daoist terms, the realisation of Dao (dedao 得道).