Satya means unfailing truth in Sanskrit. Satyadvaya refers to truth at two levels: paramārtha-satya (the ultimate truth), which is based on the absolute nature, and saṁvṛiti-satya (the conventional truth), based on worldly phenomena. This division of truth according to the level of cognition originates in the canonical Abhidharma works, where names, words, appearances, and phenomena belong to the worldly realm, and real dharmas belong to the absolute realm. In the classics of Mahayana Buddhism, satyadvaya is widely adapted into the theory that all things, empty in nature, appear as complicated phenomena. (In other words, inherent emptiness appears as bhava, or worldly existence.) Fundamental Verses on the Middle Way interprets satyadvaya in another way. It argues, “The Buddhas teach the dharma to all sentient beings according to satyadvaya.” The conventional satya (truth) refers to all names, words, expressions, and interpretations of worldly phenomena, including the teachings of the Buddha, while the ultimate satya refers to the reality beyond word and appearance. This theory influenced a number of Buddhist schools. In the Sui Dynasty, Shi Jizang (549–623), the founder of the Three-treatise School, developed the theory into “the four levels of satyadvaya.” Shi Zhiyi (538–597), the founder of the Tiantai School, proposed a theory of “the three truths” by incorporating the middle-way truth to the existing theory of the empty truth (or the ultimate truth) and the false truth (or the conventional truth).

And this is what satyadvaya means. According to paramārtha-satya, all things are empty in nature, and so there is no constant existence. According to saṁvṛiti-satya, all things appear as phenomena, and so there is no absolute nothingness. This is how we use satyadvaya to deny constant existence and absolute nothingness. (Shi Jizang: The Exegesis of Fundamental Verses on the Middle Way)