[T]he threefold truth concept, though it is not in itself discussed in detail by Chih-i, provides the hidden structure behind Chih-i’s philosophy. It is the content of Chih-i’s insight into the nature of reality. It pervades Chih-i’s lectures after his first seclusion on Mt. T’ien-t’ai, compiled as the [ Profound Meaning of the Lotus Sutra ] and [Great Concentration and Insight], and provides the key for understanding Chih-i’s interpretation of the Buddha Dharma.