In Tiantai thought, the Threefold Truth (san di) is a way of speaking about a single reality that can be discerned from three inseparable perspectives. First is the truth of emptiness (kong-di): all phenomena lack any fixed, independent essence and arise only through dependent origination. From this angle, nothing possesses a permanent self-nature, and what appears solid and enduring is ultimately insubstantial when examined in light of causes and conditions. This is the ultimate truth that undercuts attachment to any notion of inherent existence.

Yet Tiantai does not stop with emptiness alone. The second perspective is the truth of provisional or conventional existence (jia-di), which acknowledges that, although empty of inherent nature, phenomena still appear, function, and bear consequences in everyday life. Names, distinctions, moral actions, and causal relationships are treated as provisionally real and efficacious. This conventional truth allows for ethical responsibility and practical engagement with the world, without mistaking these appearances for something ultimately self-existent.

The third perspective is the truth of the Middle (zhong-di), which is the integration of emptiness and provisional existence. From this standpoint, phenomena are seen as simultaneously empty and conventionally existent, not alternating between two different states. Reality is neither exclusively empty nor simply existent as it appears; it transcends both extremes while fully including them. This Middle truth reveals that to understand any one of the three truths completely is to see all three at once, in a single, non-dual wisdom.

Tiantai master Zhiyi emphasized that these three are not separate layers of reality or sequential stages of realization, but three aspects of one and the same reality, mutually inclusive and interpenetrating. This “perfect interfusion” (yuanrong) means that emptiness, provisional existence, and the Middle are always already present in every phenomenon and every moment of experience. As a contemplative framework, the Threefold Truth guides practice toward seeing conventional appearances, their empty nature, and their Middle Way reality as a unified field, thereby avoiding both nihilism and naive realism.