The threefold truth: emptiness, provisional existence and the middle

Earlier Buddhist philosophy, associated above all with the Indian thinker Nagarjuna some centuries before Zhiyi, teaches two truths: a conventional truth, the ordinary world of things that can be named, used and spoken of in daily life, and an ultimate truth, the emptiness of any of those named things actually having a fixed, independent nature of their own. Zhiyi's Tiantai school reworked that two part scheme into three. A thing is empty of any nature belonging to it alone, exactly as the earlier teaching already held. It is nonetheless provisionally there, real enough in its own way to be named, used and spoken about meaningfully in the ordinary business of life. And the third, middle truth holds both of the first two truths at once without collapsing either one down into the other, treating emptiness and provisional existence as simultaneously and equally true of the very same thing rather than as two ranked levels where the higher truth simply cancels out or supersedes the lower one. That third, middle truth is precisely what distinguishes the Tiantai formulation from the older two truths scheme it deliberately reworks and builds upon. Zhiyi worked the doctrine out most fully in his commentary on a single verse of Nagarjuna's own writing describing dependent origination, reading that one verse as already containing all three truths at once within itself rather than treating the threefold scheme as a later addition laid on top of Nagarjuna's original teaching.

The added middle truth carries a specific philosophical consequence the older two truths scheme did not by itself require: it blocks the reading, common enough elsewhere in Buddhist thought, that the conventional, everyday world is merely a lower truth to be left behind once the higher truth of emptiness has finally been grasped by the practitioner. Because the middle truth insists that emptiness and provisional existence hold together at once rather than in a ranked sequence, phenomenal reality is not treated as a stepping stone the practitioner discards on the way toward something more real waiting beyond it. Saicho carried this threefold formulation from China to Japan in the very same transmission that also brought the three thousand realms doctrine with it, and the two teachings function together as a single, connected philosophical structure within Tendai and its later Japanese offshoots: the threefold truth is what explains, philosophically, why the ordinary world can contain the whole of reality without requiring the practitioner to renounce that ordinary world in order to reach it. Later Tiantai commentators developed the doctrine further into a claim that ordinary, unenlightened experience and enlightened experience share the very same content and differ only in how that content is recognized, a reading that later shaped Nichiren's own insistence that ordinary chanting practice could itself constitute enlightenment rather than merely prepare a practitioner for it.