The most superior contemplation, and the contemplation which is discussed in the [Great Concentration and Insight], is what Chih-i calls the “perfect and immediate cessation and contemplation.” In this case the three aspects of emptiness, conventional existence, and the Middle are contemplated simultaneously and spontaneously, and immediately perceived as being integrated, non-dual, and synonymous. As Chih-i says:

When the truths are contemplated as an object of cessation, [it is realized that] these are three truths yet one truth. When cessation is sustained by means of [insight into] the truth, [it is realized that] these are three cessations yet one cessation. For example, three aspects are present in one mental thought, and though it is one mental thought, there are three aspects present. …

When contemplating objects, the one object is a threefold object [characterized as empty, conventionally existent, and the Middle]; when contemplation is aroused by an object, it is a single contemplation yet a threefold contemplation [of emptiness, conventional existence, and the Middle]. The three eyes of Maheśvara are three eyes yet on one face. … If one contemplates [the concept of] “three yet one,” [the concept of) “one yet three” is aroused. This is beyond conceptual understanding. It is neither tentative nor real, includes neither superiority nor inferiority, has no before nor after, is not equal nor distinct, neither great nor small. Therefore it says in the Mūlamadhyamakakārikā, “Dharmas which arise through conditioned co-arising are identical to emptiness, identical to conventional existence, and identical to the Middle.” [T 46, 25b9-18]

Here threefold contemplation is explicitly defined and linked to the verse in the Mūlamadhyamakakārikā, which is the basis for Chih-i’s threefold truth concept.